ON THE 
intimate structure and history 
OF THE 
ARTICULAR CARTILAGES. 
BY JOSEPH LEIDY, M. D. 
(with two plates.) 
[Extracted from the American Journal of the Med. Bci. for April 1849.] 
The structures entering into the composition of a movable joint, or articu- 
lation of the animal body, exhibit the same wonderful adaptation to the end 
in view, which we see displayed everywhere else in nature. 
Joints are absolutely necessary to locomotion, in an animal possessing a 
skeleton or hard basis of support for the softer organs, for it is by means 
only of the different segments of the skeleton, whether internal as in the 
vertebrata, or external as in insecta, Crustacea, &c., moving upon each other, 
through the power residing in the muscles, that all locomotion is produced. 
If we conceive of one of the higher mammalia, say of man, formed with a 
skeleton in one piece, at once it alters his whole character. He becomes fixed 
to one position, the muscles ordinarily concerned in acting upon the segments 
of the skeleton are no longer of any use, and may be dispensed with. Respi- 
ration as ordinarily carried on must cease, the nerve centres concerned in 
directing the movements would be no longer required,—in fact the animal 
could not exist as such; but if its vascular system could be prolonged into a 
soil of nutritive matter, and respiration be carried on at the surface of the 
body, although ceasing to exist as an animal it would do so as a plant. 
If the skeleton be dispensed with, we may have a body capable of moving 
from place to place, by alternate contraction of different parts of the mass, 
as in a slug (Limax), but the sphere of locomotion of such an animal is neces- 
sarily very limited, and could not exist with the well characterized intelli- 
gence of an animal higher in the scale. 
The movable articulations of the human body are numerous, and present 
every variety of form of surface in their construction. The articulating sur- 
faces are usually formed upon the expanded extremities of the bones, but in 
no instance, in a normal condition, do we find the osseous structure entering 
immediately into their formation, but the opposed surfaces of the articular 
1 Leidy, Intimate Structure, etc. of Articular Cartilages. 
2 
extremities of the bones are covered by a lamina of elastic substance, the 
articular cartilage, which possesses a degree of vitality inferior to that of bone. 
To this form of cartilage I have more particularly directed my attention, and 
its history and intimate structure are the subjects of the present memoir. 
The perfectly formed or adult articular cartilages are closely moulded upon 
the articular extremities of the bones, and are inseparably adherent until 
removed by maceration in dilute muriatic or other acid, when they are readily 
detached, presenting a surface corresponding to that of the bone from which 
they were removed; being rough, and presenting beneath a lens, a number of 
ridges, conical projections and pits, all of which are for the closer adaptation 
of the structure to the bone. From the foregoing facts, these cartilages are 
called also cartilages of incrustation. 
The free surface of the articular cartilages, or that presented to the inte- 
rior of the joint is very smooth and glistening, exactly fits the surface of the 
opposed cartilage, and leaves no interval, except where interarticular carti- 
lages, or synovial doublings, are introduced, and is kept constantly bathed in 
synovia, the peculiar unctuous serous fluid of the articulations, which, added 
to the elasticity of the structure, permits these surfaces to move freely and 
easily upon each other with the least possible degree of friction and attrition, 
and with the least liability to danger of abrasion; all of which would occur to 
a comparatively great extent, if the harder and less elastic surfaces of the 
bones were to come in immediate contact. 
The articular cartilages vary in thickness in the different articulations, being 
thickest in those which are most movable, and most subject to attrition. The 
greatest thickness they reach, which is in the knee or hip-joint, is from one 
and a half to two lines. An articular cartilage also varies in thickness, in 
O / 
different parts of its extent, and thus its two surfaces are never entirely paral- 
lel with each other, for, as a general rule, upon a convex articular face of bone 
we find the cartilage forming a thin edge at its circumference, and gradually 
becoming thicker towards the centre, and upon a concave surface the reverse 
arrangement taking place, being thin in the centre, and gradually increasing in 
thickness towards the circumference, where it is again reduced to a thin edge. 
When separated from the bone, the articular cartilage may be readily bent 
double without breaking, and in fact it usually requires some force to break 
it. The course of the fracture is always perpendicular to the surfaces, and 
the broken edge presents a fibrous appearance, in the same direction, and 
in some cases it appears laminated, especially near the free surface of the car- 
tilage. 
Articular cartilages are of a pearly white colour; where thin they are 
opalescent or bluish white and translucent; sometimes they have a tinge of 
yellow, which is occasionally deepened, apparently by the imbibition of colour- 
ing matter from the synovia; more rarely they present a pinkish tinge. 
From their firmness, toughness, flexibility, and high degree of elasticity, 
besides being less liable to abrasion or other accident, the articular cartilages Leidy, Intimate Structure, etc. of Articular Cartilages. 
3 
perform an important function in diminishing the violence of blows or shocks, 
under many circumstances, serving as so many points of reaction when the 
extremities of the bones are suddenly or violently forced against one another, 
as in falls upon the feet, &c. 
They are totally non-vascular) the arterial vessels in their vicinity, after ap- 
proaching their attached surface and circumference, turn back to the venous 
trunks. The vascular circle formed at the circumference of the articular 
cartilage was called by Wm. Hunter,* the circulus articuli vasculosus. The 
blood-vessels of this circle pass a little way over the edge of the cartilage, 
and stop a little short of the angle formed by the attachment of the synovial 
membrane to the latter. These vessels are convoluted, and form loops which 
are much dilated, an arrangement first pointed out by Mr. Toynbee.y The 
vessels which approach the attached surface of the cartilage, according to Mr. 
Toynbee,J are numerous and large, and are separated from it by a delicate 
lamella of bone. 
The advantage which the articular cartilages possess in their non-vascularity 
is very great, in their immunity from the many accidents which a vascular 
tissue would be liable to in a similar position, where the parts are so much 
exposed to sources of irritation. 
Nor is it probable that lymphatics exist in them ; their vital activity is not 
very great, and if there is any interstitial destruction at all, the molecules so 
separated, may exosmose from the cartilage dissolved in the effete fluid derived 
from the nutritive fluid of the tissue. 
These cartilages are destitute of nerves;—at least they are perfectly insen- 
sible, for I have several times sliced away, wrenched, torn, and twisted the 
articular cartilage from the head of the tibia of a rabbit and a cat, without 
the animals evincing the slightest indication of pain, and although I have fol- 
lowed the course of filaments from branches of the articular nerves as far as 
the fine areolar tissue at the edge of the articular cartilages, yet I have never 
been able to detect the slightest appearance of a filament entering the carti- 
laginous structure. 
Intimate Structure of the Articular Cartilaginous Tissue.—The older anato- 
mists considered the articular cartilage to be homogeneous in its character, 
or to be composed of fibres arising from the surface of the bone, and termi- 
nating at the free surface of the cartilage, which condition was proved by the 
latter always breaking in a determinate direction, the fractured edge present- 
ing a fibrous or columnar appearance, comparable to the arrangement of the 
enamel structure upon the body of the tooth, and from its being resolvable into 
* Of the Structure and Diseases of Articular Cartilages, by Wm. Hunter, Surgeon. 
Phil. Trans., vol. xlii. 1742-43, p. 514. London. 
■\ On the Organization and Nutrition of Non-vascular Animal Tissues. Phil. Trans., 
1841, p. 159, London. 
£ Ibid., p. 173. 4 
Leidy, Intimate Structure, etc. of Articular Cartilages. 
separated filaments by maceration. How far this opinion is true will be seen 
in the course of our investigations. 
When a thin section of the articular cartilage is submitted to the micro- 
scope, two distinct parts, or structures, are observable in it; organic cells, or 
cartilage cells or corpuscles, and an intercellular substance, or matrix.* 
Cartilage Corpuscles, (Plates I. and 11.)—These bodies are solid nucleolo- 
nucleated cells, imbedded in the cartilage matrix, and varying in a slight de- 
gree in different parts of the articular cartilage. A few of them are single 
or isolated, but most usually they are found in groups of two, up to twenty- 
two, the latter being the highest number I met with. The groups are 
arranged in single, double, triple, or quadruple rows, the direction of which, 
in the deep part of the cartilage, or that nearest the surface of attachment, is 
perpendicular (Plate I. Fig- 1, e) to the surfaces, for the most part, but as 
they approach the free surface, they become more or less oblique (d) and 
even irregular, and finally, near the free surface, become parallel (c) with the 
latter, or at right angles with the deeper groups. The arrangement of the 
cell groups is considered by most modern anatomists to be the cause of frac- 
ture of the cartilage, in a determinate direction; perpendicular to the sur- 
faces in the deeper part, and parallel with the same at the free surface. The 
groups of cells are comparatively few in number in the deep part of the car- 
tilage, or the intervening matrix is in greater abundance, but they gradually 
increase in number as they approach the free surface, near which they are 
found quite crowded, and with little intervening matrix. 
The deeper groups (Plate I. Figs. 2 and 8) of cells are composed of a greater 
number of individual cells, than those existing more superficially, and in the 
stratum of cartilage forming the free surface, (Plate 11. Fig. 1,) single or iso- 
lated cells are more numerous than in any other part of the cartilage, and the 
most frequent groups are composed of two or three cells,—rarely a group con- 
taining more than six is found. 
The cells when single or isolated, are round or elliptical in outline, but when 
grouped, they are flattened or have the appearance of compression upon the 
sides presented to each other, and rounded at the circumference of the group, 
with the two end cells frequently elongated, or even brought to a point. 
* A striking analogy exists between the articular cartilaginous structure, and some of 
the algous forms of vegetable life; thus, the Conferva mucosa ? Mert, (Harvey, Manual 
British Alga, London, 1841,) which is found growing in the little stream running through 
the swamp at Kaign’s Point, N. J,, just below Philadelphia, consists of filaments or 
rows of cells enveloped in a transparent mucoid substance, corresponding to the cell groups 
and matrix of the articular cartilage. The cells are sometimes filled with endochrome, 
in other instances the latter is contracted into a mass occupying the centre of the cell, 
while the interspace is filled with transparent matter, and the endochrome contains a 
nucleus rendered visible by iodine, in all which respects exhibiting a resemblance to 
the analogous points of structure of articular cartilage. Leidy, Intimate Structure, etc. of Articular Cartilages. 
5 
In the deeper part of the cartilage, the diameter of the cells in different 
directions varies hut little, and averages the o cio o^l °f an inch in their long 
diameter, and the of an inch in their shortest diameter; but in the 
superficial stratum of cartilage, the cells or groups of cells (Plate 11. Pig. 1, 
and Fig- 2, a) are much flattened parallel with the surfaces of the cartilage, 
appear large and broad when viewed in this direction, and measure upon an 
average the of an inch long, while the edges of the cells or groups, when 
viewed in a vertical section of the cartilage (Plate 11. Fig. 2 h, and Fig. 3,) 
appear very narrow and lenticulo-linear in outline, and measure in thickness 
on an average ~Toth 0f an inch. 
When a thin section of the cartilage is viewed beneath the microscope, the 
cell-groups are observed to produce a shaded ring, in their vicinity, in the 
matrix, and when well-defined, they appear surrounded by a clearer or more 
translucent wall or outline than the matrix; but when within the focus a little, 
they appear surrounded by a dark outline or boundary. The outlines of the 
individual cells, where they approach, or are in contact in the groups, are often 
indistinct, but may always be distinguished by a shaded line passing in and 
indicating the interval. 
In structure, the cells present points of difference in different parts of the 
cartilage. 
The cell wall appears blended or fused with the intercellular substance, and 
can be studied as a distinct structure only in the very early condition of the 
cell. 
The cell contents (Plate I. Figs. 2 and 3) usually consists of a translucent 
homogeneous, or at most an indistinctly and very minutely granular substance, 
with a more or less central mass of distinctly coarser and darker granular 
matter, which is generally considered to be the nucleus, but the true character 
of which will be indicated hereafter. This mass contains a transparent, round 
or oval nucleus, which is brought into view and coloured brown, by the appli- 
cation of tincture of iodine. The mass also frequently contains fat granules 
or globules. It is larger in the more superficial than in the deeper cells, mea- 
suring in the former on an average the both of an inch in diameter, in the 
latter, the g-jVfth °f an inch- Generally the more superficial layers of cells 
have not this isolated mass, but are filled (Plate 11. Figs. 1, 2, and 3) 
with finely granular contents interspersed with numerous darker and well-de- 
fined granules measuring about the °f an inch. These granules have 
a black outline, resembling very much fine fat granules, and some of them 
appear to be really such, for after macerating the cartilage a few days in water, 
I have noticed a number of them to become aggregated into one or more glo- 
bules having all the appearances of oil. In these superficial cells the nucleus 
is large and distinct, round or elliptical, very finely but distinctly granular, 
and contains about its centre a transparent, but often indistinct nucleolus. In 
some instances I have noticed the larger and distinct granules of the last men- 
tioned cells forming a circle (Plate 11. Figs. 1, 2, and 3), more or less broken 6 
Leidy, Intimate Structure, etc. of Articular Cartilages. 
or defined, a short distance from the nucleus, and giving the latter the appear- 
ance as if contained within a larger hut much less distinct nuclear body. 
Sometimes this arrangement is quite distinct, but usually it can be but faintly 
seen. 
In other cases the cells of the superficial stratum of the cartilage present 
the same appearance as the deeper cells, excepting that they are more flat- 
tened in a direction parallel to the surface, and the interior granular mass is 
larger. 
In not unfrequent instances, I have noticed in the most superficial stratum 
of some of the articular cartilages, large, flattened cells, or cell-groups, some- 
times with the outline indistinctly delineated, and with nothing distinguish- 
able, excepting finely and indistinctly granular contents, appearing like cells 
which have been rubbed out in the attrition of the opposed surfaces of the 
cartilages. 
Less frequently I have observed immediately beneath the free surface of 
the cartilage, and too deep to be influenced by friction, cells (Plate I. Figs. 
7 and 8) large and flattened, most usually isolated, or in pairs, finely and in- 
distinctly granular, without apparent nucleus or other more distinct body, or 
with the apparent formation of a nucleus from the aggregation of the finer 
granules around a larger, transparent, and very distinct granule or nucleolus. 
The nuclear appearance was most distinct in the paired cells. What is the 
character of this variety of articular cartilage cells? Are they cells in the 
process of development? 
Cartilage Matrix, or the intercellular substance of the articular carti- 
lage is, as previously mentioned, in comparison with the cartilage corpuscles, 
most abundant in its deeper part. It is in thin sections translucent, but not 
to the same extent as the cell contents between the cell wall and central mass, 
when the latter exists, and it usually has a faint yellowish hue. Most com- 
monly it has a more or less finely granular appearance, and has generally been 
described as a homogeneous hyaline, or a finely granular substance, but 
although it may have the latter as an ultimate arrangement, yet from nume- 
rous and carefully repeated observations, I am fully convinced that it has a 
filamentous structure.* These filaments (Plate I. Fig. 4) are exceedingly fine, 
but possess considerable strength, and are pretty uniform in size, having an 
average measurement of the of an inch in diameter. The largest I 
measured, which are few in number, measured the owg-th of an inch, the 
smallest, the 3010ot'1 an inch. When viewed by light thrown upon them 
with considerable obliquity, they appear faintly granular, each filament com- 
posed of a single row of very fine granules. Acetic acid produces no apparent 
influence upon them; potassa renders them more translucent and faint; and 
iodine stains them yellow. 
* Proceedings Academy of Natural Sciences of Philadelphia, vol. iv. No. vi., 1848. Leidy, Intimate Structure, etc. of Articular Cartilages. 
7 
These filaments lie parallel with one another, they adhere very tenaciously 
together and under ordinary circumstances are hardly demonstrable, although 
I have occasionally seen them at the ends of a torn shred of articular cartilage. 
But if an articular cartilage be taken from a bone which has undergone 
maceration in diluted muriatic acid to remove its earthy constituents, and be 
broken, and from the fractured edge a fibre or shred delicate enough to trans- 
mit light, be torn off with a pair of fine-pointed forceps, and be submitted in the 
ordinary manner to the microscope, using the one-fourth or one-twelfth of an 
inch object glass, numerous, detached and exceedingly delicate, spider-thread- 
like filaments will be readily detected along the whole length of the sides of 
the shred. In making this observation it may be frequently noticed, that 
in tearing off fine shreds of the cartilage, if a group of cells has been in the 
course of the rupture, it will be torn through, which alone would be sufficient 
to indicate that the fracture of articular cartilage in a definite direction does not 
depend upon the arrangement of the cell groups. Besides this, straight fibres 
are frequently torn loose in the deeper part of the cartilage where the matrix 
is most abundant without coming in contact on either side with cell groups, 
and it is now sufficiently evident that the latter have little or no influence in 
determining the course of fracture, but that it is entirely due to the filament- 
ary arrangement of the matrix. 
This filamentous structure of the articular cartilages, though not so inti- 
mately understood as presented above, was nevertheless pretty satisfactorily 
known to exist; “ thus,” Wm. Hunter says, “we may compare the texture of 
a cartilage (articular) to the pile of velvet, its fibres rising up from the bone, 
as the silky threads of that rise from the woven cloth or basis;”* and M. de 
Lasone also says, “si Ton veut examiner le cartilage qui encroute la tete du 
femur, il faut commencer par diviser verticalement cette tete en deux parties, 
et les soumettro ensuite ala coction; alors on recommit que I’arcade ou Pes- 
pece de ceintre que forme la portion cartilagineuse qui encroute I’os, n’est 
qu’une multitude des petits filets adosses et lies les unes aux autres, tous per- 
pendiculaires au plan de l’os.”f Mr. W. Hunter also supposed the perpendi- 
cular fibres to be held together by transverse ones so as to “make the whole 
a solid body,” and these “ being very tender,” in macerating the cartilage, 
they are destroyed, leaving the perpendicular ones detached from one another. 
No filaments of this character are to be detected by means of the microscope. 
It is well known that if an articular cartilage be forcibly broken through, 
the fragments will adhere by a thin stratum of membrane covering its free 
surface. This membranous layer is readily detached by tearing the fragments 
from each other, and it was considered by the older anatomists to be the syno- 
vial membrane. Having all the characters of cartilage, its disposition by 
• On ths Structure and Diseases of Articular Cartilages. By Wm. Hunter, Surgeon. 
Philosoph. Transac., vol. xlii. p. 514. London, 1742, ’43. 
■\ Second Memoire sur I’organisation des os. Par. M. de Lasone. Mem. de I’Acad. 
Roy. des Sci., tom. 69, Paris, 1752. 8 
Lcidy, Intimate Structure, etc. of Articular Cartilages.'' 
modern anatomists, is believed to depend upon the arrangement of its cell 
groups, which, as before mentioned, are parallel to the free surface of the 
cartilage. But instead of its membraniform condition depending upon the 
course of its cell groups I find it to result from the structure of its matrix, 
which has also a filamentary arrangement like that of the deeper part of the 
cartilage, the filaments, however, taking a course at right angles to those of the 
deeper cartilage and parallel to the surface. 
In neither case, then, do the groups or columns of cells determine the course 
of rupture of the articular cartilage, but on the contrary, it is the filamentary 
arrangement of the cartilaginous matrix which influences the direction of the 
ceil groups, for in the development of the latter, from the division of the primi- 
tive or original cartilage cells, they take the direction in which there is least 
resistance, which would be in the direction of the length of the filaments of 
the matrix; hence, in the deeper part of the articular cartilage, as a general 
rule, we find the cell groups and filaments of the matrix both vertical to the 
surface but, in the superficial stratum, they are parallel to the surface or at 
right angles to the former. 
Synovial Membrane in its Relation to the Articular Cartilage.—lt has been 
a subject of much discussion among anatomists whether the free surface of the 
articular cartilage is covered by a reflection of the synovial membrane or not. 
Win. Hunter, Soemmering, Bichat, and many others assert and have tried to 
demonstrate its existence, but they have evidently mistaken the lamina of carti- 
lage forming the free surface of the articular cartilage for it, while Cruveilhier, 
Magendie, Yelpeau, &c., doubt its existence from pathological and physiological 
observations. In my observations I have always failed to detect the slightest 
trace of synovial membrane, in the adult, upon the free surface of the articular 
cartilage, or even the appearance of a basement membrane; for in all eases, 
no matter how thin the lamina was which was torn from the articular surface, 
it presented the indistinctly granular, or, when treated as I have before men- 
tioned, the finely filamentous structure of the cartilage matrix. It appears to 
terminate at the circumference of the articular cartilage a very little beyond 
or in advance of the circulus articuli vasculosus. In the foetal state it exists 
in a very distinct state, covering the surface of the epiphysal cartilages, and 
may be readily distinguished by its flattened epithelial, nucleated cells, be- 
neath which can also be readily detected a transparent, homogeneous base- 
ment membrane. But after birth in the progress of growth of the articular 
cartilages, it appears to be destroyed by pressure and attrition and probably 
from the retiring of the surface vessels towards the circumference. It appears 
to be progressively removed from the centre to the circumference of the carti- 
lage, but always to remain a little in advance of the circulus articuli vascu- 
losus. 
Occasional Peculiarities in the Structure of the Articular Cartilages,—ln Leidy, Intimate Structure, etc. of Articular Cartilages. 
9 
several instances, I have noticed in some of these cartilages what appeared to me 
to he numerous minute lacuna;, and I have now in my possession an articular 
cartilage (Plate I. Pigs. 2 and 4) from the condyles of an os femoris exhibiting 
this structure. They exist in greatest abundance in the deeper part of the 
cartilage, gradually decrease in number, as the free surface is approached, and 
disappear entirely in the superficial fourth of the cartilage. They are lenti- 
cular in outline, invariably situated with their long diameter parallel to the 
surfaces of the cartilage, or at right angles to the filamentary intercellular 
substance, in which they are directly placed. The longest measure the 
of an inch, the shortest the jT'¥Tth of an inch; the short diameter is about the 
~s Q-th of an inch. When well defined, beneath the microscope, they appear 
more translucent than the cartilaginous matrix in which they are situated, and 
when viewed a little within the focus of the instrument, they appear deep 
black, or oppose the transmission of all light. 
Another peculiarity (Plate I. Pigs. 5 and 6) which I have occasionally no- 
ticed, is the existence of fibres or columns of bone penetrating the structure of 
the cartilage,—I have in my possession an articular cartilage from the head 
of an os femoris presenting this character. These fibres are generally found per- 
vading the cartilage near its surface of attachment, but are not the continuation 
of the bony structure upon which the cartilage is placed, for they are invariably 
arranged in a direction parallel to the surfaces. They are quite uniform in 
shape and structure, being compressed, cylindrical, in transverse section pre- 
senting an elliptical figure the long diameter of which is placed parallel to 
the surfaces of the cartilage or at right angles to the filaments of the matrix 
in which they are situated. They are not numerous, and vary from a size 
not exceeding a cell group of five cells to the size of four or five such groups. 
They are concentrically laminated, and also present a radiated conformation, 
resembling somewhat the structure of an Haversian ossicle, but neither present 
the canal nor the Purkinjean corpuscles. 
Development and Growth of the Articular Cartilages.—The articular carti- 
lages as a distinct structure are not perceptible so long as the epiphyses and 
articular extremities of the bones are not ossified, consequently they do not 
exist during foetal life or for a considerable period after birth. At birth if 
an epiphysal extremity of a long hone be cut vertically through, it will be 
observed that the cartilage of the epiphyses extends to the synovial membrane 
and that there is not the slightest trace of a line of demarcation between the 
two varieties of cartilage. If the section be more carefully examined, a 
number of branching canals will be observed ramifying through the carti- 
lage, many of which approach its articular surface but are in all cases sepa- 
rated from it by a thin lamina of the cartilage containing no canals. This 
thin lamina is the first appearance of the articular cartilage, but presents no 
distinction of structure at this period from the mass of cartilage of the epi- 
physis. The canals of the epiphysal cartilage contain blood-vessels, which, 10 
Leidy, Intimate Structure, etc. of Articular Cartilages. 
according to Mr. Toynbee,* have a very peculiar disposition, consisting of ar- 
teries terminating in dilatations, or in convoluted branches, from which the 
veins arise. In the process of ossification and increase in size of the epi- 
physal cartilage, the developing articular cartilage appears to be pushed 
before it, resulting from an interstitial growth depending upon the division of 
the primary cartilage cells, the probable development of others, and the in- 
crease of the matrix or intercellular substance. When the articular surface 
cartilage (Plate 11. Fig. 5) of a cartilaginous epiphysis is examined micro- 
scopically, it is found to have all the characters of the latter, and at an 
early period of foetal life consists of a translucent, hyaline substance, in which 
are diffused with considerable uniformity, rounded or elliptical, isolated, nu- 
cleolo-nucleated cells, separated from one another by interspaces less than 
their own diameter. They vary to a moderate degree in size, and average 
about the 1 jth of an inch in diameter. The cell contents forms a mass rather 
darker than the intercellular matrix, the reverse of what is the case in the 
perfected articular cartilage. It is finely granular, with an intermixture of 
coarser and more defined grannies, some of which appear to be oleic in cha- 
racter. The nucleus is round or oval, varies a little in diameter, averaging 
about the ?L_th of an inch, and is very finely granular in structure. Some- 
times there are two nuclei, sometimes separated and distant, at others, ap- 
proached, flattened upon the opposed sides, and apparently having originated 
from the division of a single nucleus. The nucleus contains a more consist- 
ent, translucent nucleolus, readily brought into view by the tincture of iodine, 
and measuring about the fT-[TT th of an inch. The intercellular substance is 
comparatively soft, very translucent, and homogeneous. As the articular car- 
tilage advances in its development, the intercellular matrix increases in quan- 
tity, separating the cells at greater distances apart, and acquires a firmer con- 
sistence. It becomes faintly granular, which after a time becomes more 
decided, though indistinct at any time without a good defining power, and 
finally takes on the peculiar filamentous arrangement described in a previous 
part of this memoir. 
But the question arises how does this intercellular substance increase in 
quantity ? Is it a direct deposit of imbibed matter from the liquor sanguinis 
in the vicinity of the cartilage, or is it produced through the agency of the 
cartilage corpuscles, or organic cells of the tissue ? Kecollecting that 
the liquor sanguinis does not contain dissolved cartilage, it cannot be a 
direct deposit; but may not the cartilaginous molecules already produced, 
convert an assimilative substance into molecules of a similar character, chemi- 
cal and physical ? The latter is probable, but it is easier to suppose it to be 
formed from imbibed albumen, through the agency of the cartilage cells, in the 
same manner that it originally results from the albumen ovi, probably through 
the agency of cells, the earliest cartilage cells, which have been the offspring 
retaining part of the organizing force of the Purkinjean vesicle. As it is 
* Phil. Trans., 1841, p. 166. Leidy, Intimate Structure, etc. of Articular Cartilages. 
11 
certain that cartilage tissue is produced from albumen, it is worthy of inquiry 
whether the organic cells of the cartilage are capable of fixing a material 
thus transformed in their vicinity. If it can be demonstrated that such a 
power exists in organic cells in any part of the organic kingdom, we may 
feel assured that it prevails throughout. Turning back then, in vitality's 
great book, to the first few pages, we discover some very simple expositors of 
the question at issue. Thus, if we examine several of the families of Chloro- 
Spermeae, the oscillatorim, ulvaceae, nostochinem, &c., we find numerous zooid 
plants, some of the simplest forms in the organic kingdom, consisting of single 
rows of organic cells, enveloped in a mucoid substance, and swimming in water 
or flourishing in humid situations. When the green spores, single organic 
cells filled with endochrome and containing a nucleus, are discharged from a 
parent cell, they accumulate and fix around themselves a mass of mucoid sub- 
stance from the nutritive matter floating in the element around them. The 
spore develops a perfect plant, a mere filament or row, or a lamina of cells, 
continues to accumulate mucoid matter around it, until the latter is frequently 
several times the diameter of the plant itself. Retaining its organic activity 
it produces spores, which are to be discharged, and undergo the same progres- 
sive changes. Perceiving, then, that these cells can collect and fix matter 
around them, and continue to operate upon imbibed nutritive fluid, it is ren- 
dered probable that an analogous process may be carried on in the denser car- 
tilage, since the latter, as is well known, is capable of imbibing nutritive 
fluid. 
Whether the surrounding matter is formed within the cells and then exos- 
mosed, or whether the cell life extends its formative power beyond the pre- 
cincts of the cell wall, remains a question, but I think both are probable. 
The cartilage cells at the early period of development are easily detached 
from the matrix, but at a later period the cell wall fuses or blends itself with 
the intercellular substance, but even after this the granular cell contents is easily 
detached in a single mass (Plate 11. Pig. 4), appearing to be retained together 
by a delicate protoplasmatic envelop, corresponding to the primordial utricle 
of vegetable cells. Of the existence of such a structure in some animal cells 
I am well convinced, and hope to prove in a future memoir on the subject. 
After the cartilage matrix has taken on itself the granulo-filamentous struc- 
ture, the cartilage cells increase in number by division, and probably also by 
the origination of new cells. In studying the development of the groups 
of cells of the perfected articular cartilage, the steps of progress, as noticed 
at several periods during the growth of the latter, appear to be as follows: 
The simple isolated cartilage cells are found to become somewhat elongated, 
(Plate 11. Fig. 6,) then at the sides to present the appearance of an indentation. 
The nucleus has a central position, and then a faint dividing line, (PI. 11. Fig. 
7,) more translucent than the other parts of the cell, is observed crossing the 
short diameter of the cell, resembling somewhat the transverse line of dehis- 
cence of an ovisac. By varying the focus of the microscope, it is found that this 12 
Leidy, Intimate Structure, etc. of Articular Cartilages. 
line penetrates as a plane through the cell. The next change (Plate 11. Figs. 
8 and 11) which is remarked, is the retiring of the granular cell contents 
from the inner parietes of the cell wall, excepting where in contact with the 
dividing line of the cell. The cell wall has now become blended with the 
intercellular substance, and the latter also occupies a position between the 
inner surface of the cell wall, with which it also blends, and the retiring cell 
contents. The cell contents, (Plate 11. Fig. 9,) at this period distinctly 
presents itself divided into two masses, corresponding to the previously men- 
tioned line passing through the cell, and each mass contracts itself with the 
contained half of the original nucleus, towards the centre of its respective cell. 
From the uniformity with which the granular cell contents contracts, hold- 
ing all its contained parts together, granules, nucleus, and fat globules, I am 
strongly impressed with the idea that it has a protoplasmatic envelop or 
primordial utricle. In vegetable cells we frequently observe the same mode 
of retiring of the granules of endochrome retained together by the delicate, 
transparent, mucoid envelop, the primordial utricle, and, as is well known, 
this may be produced by artificial means, which I find to be also the case with 
the cartilage cells, for I have observed the cell contents slightly and very gra- 
dually contract in a single mass upon the application of tincture of iodine, or 
even under the long-continued imbibition of water. 
Whether the division of the nucleus precedes that of the cell, or the re- 
verse, still remains a problem. Cartilage cells are not unfrequently observed 
containing a nucleus apparently in progress of division, and others, with a 
pair of nuclei near each other, and flattened upon the opposed sides, having 
the appearance as if the result of division of a primitive nucleus, without the 
slightest trace of any disposition of the cells to divide themselves. In other 
instances I have detected cells presenting a slight parietal indentation, without 
•any similar appearance of the nucleus, and in all other cases, when the cell 
exhibited signs of division, a corresponding change was invariably observed in 
the nucleus. 
The pair of cartilage cells which have originated from the primary cell, 
increase in size by the assimilation of nutritive matter, and undergo the same 
division as just described, until groups are formed as found existing in the 
perfected cartilage. The cell contents continually retire, but at the same 
time appear to partake in the general nutrition of the cell, until in the cell 
group we find the masses generally central, frequently irregular in outline, 
and containing more or less oil globules, and one or two nuclei, and in this state 
have been generally mistaken for the nuclei of the cartilage cells. 
The cells, in their progressive division, do so generally in the same line, but 
also very frequently divide, laterally, so that the pair of cells resulting from 
the division of the first, may either form a row (Plate 11. Figs. 12 and 13) 
of four or a group of four, (Plate 11. Fig. 10,) and continue in this manner. 
The cause determining the arrangement of the cells into rows instead of Leidy, Intimate Structure, etc. of Articular Cartilages. 
13 
masses, lias already been referred to • the least resistance to their extension 
being parallel with the filaments of the cartilage matrix. 
The irregularity which exists in certain of the cell groups, especially in the 
stratum lying about one-fifth the thickness of the articular cartilage below its 
free surface, probably depends in some degree upon the pressure of the opposed 
cartilages of the joints. Ido not mean by this that a sudden push would knock 
the deeper groups out of a vertical line, but I think during the progress of 
division of the cells and extension of the groups, a frequently repeated or 
moderately continued pressure exerted upon the free surface of the cartilage, 
would- give them a tendency to incline to one or the other side, and hence 
their obliquity, or curved or irregular character from the ordinary line in a 
part of the cartilage most influenced by the pressure. 
Of the Nutrition of the Articular Cartilages.—lt has been already suffi- 
ciently proved (by the continual of the intercellular substance, and 
division and increase in size of the cartilage cells), that during its develop- 
ment and growth, the articular cartilage possesses an interstitial nutrition, but 
the question arises, after the cartilage is fully formed, is there a constant inter- 
stitial waste and repair of the cartilaginous element, as is the case in most 
organic tissues ? M. Cruveilhier says, u les cartilages diarthrodiaux ne pre- 
sented aucune trace d’organisation,”* from which assertion it is evident that 
the existence of blood-vessels in a structure, is considered the necessity of 
organization, an error into which the older anatomists continually fell into. 
But we now are certain that these are only a provision for carrying a nutritive 
material within the sphere of action of those bodies which are the grand cha- 
racteristic of organization, the organic cells, and that they are not necessary 
to organization, or even organic activity, but only to particular forms of it. It 
is the constant supply of a nutritive fluid which is essential to the active con- 
dition of the vital force residing in the organic cells, no matter whether the 
fluid be conveyed to them by channels (blood-vessels) excavated in the mass, 
or whether it be obtained by imbibition from the surface of the latter. Does 
not the stomach of a Hydra prepare a fluid as capable of digesting materials 
as that of man? and although the entire animal does not possess a single 
blood-vessel, who will say that this organ presents less the phenomena of 
organization than the corresponding one in man? 
When an animal or plant is small, simple in structure, or possesses few and 
minute, or very simple organs, it is sufficient that the body or organs be 
bathed in a nutritive fluid, from the surfaces of which it may be imbibed, to 
present all the phenomena of vital action; but when the being becomes mass- 
ive or complex, from numerous organs which are massive, blood-vessels be- 
come necessary, or rather channels which divide the masses into a surface of 
contact for the nutritious fluid, of greater or lesser extent, depending upon the 
* Obs. sur les Cart. Diarth., Arch. Gen. de Med., vol. iv. p. 162. 14 
Leidy, Intimate Structure, etc. of Articular Cartilages. 
degree of organic activity displayed by the organs, which is indicated by the 
amount of nutritive fluid they require. 
If, then, we perceive an algous plant, or simply constructed animal, capable 
of obtaining nutritive matter from the water in which they are bathed, or the 
lichen from the rarer atmosphere in which it exists, without blood-vessels per- 
vading their structure, is it not probable that in more complex animals we may 
have simple structures nourished in a similar manner ? The articular carti- 
lage appears to be such an one, without blood-vessels it is bathed by fluid ex- 
osmosing from the vessels beneath its attached surface, from the circulus vascu- 
losus at its circumference, and especially by the synovia upon its free surface. 
I have said especially the synovia, an idea which may at first view appear 
preposterous, but which with a little consideration will appear at least quite 
probable. 
We find all the conditions of a nutritive fluid due to the articular cartilage 
in the synovia, and it is particularly jjch in albumen, the main element of 
nutrition of the cartilage. 
From several experiments I find the articular cartilages are quite capable of 
imbibing the synovial fluid. Thus I collected the synovia from several joints 
of a calf in a vessel, and upon drying an articular cartilage, and then immers- 
ing it in the synovia, I found it gradually to imbibe the fluid, and resume its 
former appearance. Somewhat similar experiments I tried upon several living 
animals,—a rabbit and a pigeon. When a joint was opened, and the articular 
extremity of the bone protruded and allowed to dry, which it does pretty 
rapidly, upon reducing the dislocation, and examining it again after a little 
while, and cutting vertically through the articular cartilage, I found it had 
imbibed fluid from both surfaces, while a thin layer on the interior was still 
dry. 
•s Another experiment showed me that imbibition takes place with consider- 
able power in this tissue. I took four pieces of articular cartilage, each about 
one inch square, and two lines in thickness, permitted them to dry, by which 
they shrunk to a little more than one line in thickness, placed them in a vessel 
of water, and rested upon them a stage loaded with nearly ten pounds. The 
next day, upon removing the stage, I found the pieces had resumed their 
former bulk, thus having imbibed the water with a power sufficient to raise 
ten pounds nearly one line, and I have no doubt the power is much greater, 
but how much more so, it was not convenient at the time of my experiment 
to determine. 
But, besides mere imbibition, we have all the conditions of that remarkable 
modification of the phenomenon, endosmosis, present in the articular cartilage, 
and even to its greatest intensity. Dutrochet proved long ago that albumen 
dissolved in water produces endosmosis with a degree of force not paralleled 
by any other organic substance, under ordinary circumstances. 
The synovia presents a highly inspissated albuminous fluid separated by the 
articular cartilage from the much thinner liquor sanguinis of the vessels be- ' Lcidy, Intimate Structure, etc. of Articular Cartilages. 
15 
neatli. In sucli a condition, having proved the power of Imbibition of syno- 
via in the living animal, a constant endosmosing current must exist from with- 
out, and an exosmosing one from within. 
Having introduced some saturated solution of ferrocyanide of potassium 
into the articulation of the knee of a living rabbit, a short time after it was 
indicated in the interior of the tibia by producing a precipitate with sulphate 
of iron. The same, experiment I repeated upon a pigeon, and with like 
results. 
During the passage of the currents of fluid through the articular cartilage, 
nutritive or organizahle in character, if any activity still exists in the life seats, 
the phenomena of nutrition must he the result. 
From the microscopic appearance of the cartilage, we observe that from 
various interstitial changes, the organic cells must retain at least a part of their 
wonted activity. 
When we consider the amount of rubbing of one articular surface upon 
another in a movable joint, like that of the knee or hip, under the pressure 
of the superincumbent mass, from year to year, we cannot help thinking that 
the wear of the articular cartilages must be more considerable than is gene- 
rally supposed, although we really perceive but the slightest degree of diminu- 
tion after a lapse of many years, and even in advanced age, I have frequently 
noticed hardly any decrease in their thickness. The soft lips of the devotee 
in a few years will leave a deep impression upon a sacred marble, and I think 
a walk of some miles per day, through several years, will detach molecules 
enough from the surface of the articular cartilages, although they are kept 
constantly lubricated by a substance so well adapted to remove friction, to re- 
quire a renewal of structure through the process of nutrition. 
That such a repair is constantly going on is also rendered probable, by the 
condition of the more superficial stratum of the articular cartilage, in which 
are found cells presenting the appearance of having been later formed than 
those more deeply situated, and this becomes more strikingly the case as we 
approach the free surface of the cartilage. In the deep part of the carti- 
lage the cell groups are large, the cells are apparently much diminished 
in organic power by frequent division, and the intercellular matrix is abun- 
dant, all betokening an earlier formation than the part lying more superficial 
to it, in which latter the cells are apparently in the progress of subdivision and 
formation of groups, and the matrix in comparatively small quantity, like in 
early cartilage. And then the occasional appearance of the development of 
new cells in the more superficial cartilage, will still favour the idea of an in- 
terstitial nutrition, which though slow, is sufficient to compensate for the wear 
of the cartilage. 
Pathological Conditions of the Articular Cartilages.—As the articular car- 
tilage contains no blood-vessels, so it is not liable to inflammation • but we 
frequently find cases in which there is an appearance of ulceration or corro- 16 
Leidy, Intimate Structure, etc. of Articular Cartilages. 
« 
sion of tlic surface of less or greater extent, or it may present numerous 
minute, disconnected fibres projecting from the surface of the hone, like the 
pile of velvet, or it may be entirely removed. All these changes may take 
place from either surface of the articular cartilage. The most prevailing opin- 
ion among pathologists of the present day is that these changes are the 
result of solution generally in purulent matter, and from the observations of 
Cruveilhier, it appears they are more rapid if the fluid acting upon the car- 
tilage is in a state of putrescence. While the cartilage is bathed in pus, 
from the catalyso-disorganizing nature of the latter, it may be gradually cor- 
roded away from the surface, and from an exosmotic current of the seroid 
fluid of probably modified pus (scrofulous), filaments may be dissolved out and 
cell groups detached, or probably disorganized and dissolved out, leaving the 
remainder of the cartilage in the form of a layer of disconnected filaments, like 
the pile of velvet, as already alluded to. Should the pus or other catalyso- 
disorganizing fluid (modified synovia) become putrescent, then must the de- 
struction of the cartilaginous structure be necessarily more rapid, not only 
from the same action being instituted in the molecules forming the surface 
of the cartilage, but from imbibition; it will also set up the same action 
interstitially, and will be aided by the death of the life centres, the cartilage 
cells, for putrescence is ever deleterious and destructive to cell life. Even the 
infusorial animalcule and algous plants, which are generally believed to thrive 
most in water with putrescent organic matter, with the exception probably of 
Monads and Vibrios, are absolutely destroyed by it, and it is not until the 
putrid exhalations cease, that they become developed within the fluid. So 
long as a lamina of cartilage is lefy upon the surfaces of the bones of a 
joint, and the life of the cartilage ceils be not destroyed, it is probable there 
may be the power existing of a very slow regeneration of lost substance, but 
if the cartilage be entirely removed, as the agents of its formation, the cells, 
are gone, there can be no restoration. If the bony surfaces be exposed, and 
pus or other catalyso-disorganizing fluid be present, the destruction of the 
bones is the result; if the formation of such fluid cease, and what has been 
formed is removed, and effusion of fibrin from the vessels of the osseous struc- 
ture takes place from subsequent organization and deposit of osseous salts in 
the latter, we may have anchylosis, or irregular exostoses. If fibrinous mat- 
ter be not effused, from the movement of one bony surface upon the other, 
the excited vessels of the osseous structure may deposit a lamina upon the 
rubbing surface as hard as dentine, and which from continued friction be- 
comes highly polished, 
In the rupture of an articular cartilage it is said the fragments never unite, 
which fact was formerly frequently advanced in support of the non-organiza- 
tion of the tissue. Muscular substance, when destroyed by violence, is not 
restored; a lichen cut into two will not unite at the edges; nor will algous 
plants unite when divided. The nutrition of the parts continues, as is the 
case with the fragments of the articular cartilage, but as well almost might the Tlatr d. 
Joseph T/eldy, del- 
T. SiruZairs. lith.ThiU' TLatt JI 
Joseph I e*xty, deJ . 
T. Sinclaxrs, lith/. ThiZ? Leidy, Intimate Structure, etc. of Articular Cartilages. 
17 
two opposed surfaces of articular cartilage unite in a joint in which there is 
little motion, as for the two broken edges of one to do so. 
When granulations occur upon the surface of an articular cartilage, which 
is extremely rare, they arise probably from the elfusion of fibrin from the cir- 
culus vasculosus of the joint, extending upon the surface of the cartilage and 
agglutinated to it. 
REFERENCE TO THE FIGURES.—PLATE I. 
Fig. 1 represents a vertical section of the articular cartilage of the head of the os 
humeri, highly magnified, a, free surface of the articular cartilage; b, surface of attach- 
ment’; c, superficial stratum of cartilage in which the groups of cells are parallel 
with the free surface; d, stratum in which the course of the cell groups is irregular; e, 
deeper part of the cartilage, exhibiting the general vertical position of the cell groups, 
and the comparatively large quantity of intercellular substance. 
Fig. 2. A cell group from the deeper part of the articular cartilage of the condyles of 
the os femoris, very highly magnified. It consists of a single row of cells, and does not 
present so straight a course as usual. In the interior of the cells may be observed the 
contracted mass of granular contents containing one or two small nuclei, and more or 
less fat globules, a, represents one of the lacunae, which I have occasionally noticed 
in the matrix of articular cartilage. 
Fig. 3. A group consisting of three rows of cells, from the deep part of the articular 
cartilage of the head of the os femoris, very highly magnified. In several of the cells, 
as well as in some of those of the preceding figure, some clear globules will be noticed 
which have the appearance as if they had escaped from the central granular mass. 
Fig. 4 represents a shred of cartilage, torn from the deep part of an articular carti- 
lage from the condyles of the os femoris, prepared as stated in the memoir, highly 
magnified, and exhibiting particularly the filamentary structure of the cartilage matrix. 
Some of the peculiar lacunse are also represented, as this specimen contains them. A 
vertical group of cells is also figured. 
Fig. 5. Yertical section from the deepest part of an articular cartilage of the head of 
the os femoris, highly magnified, and exhibiting several groups of cartilage cells, and 
also the transverse section of three of those peculiar fibres of bone, occasionally found 
pervading the cartilaginous structure, presenting the appearance of their interior struc- 
ture. 
Fig. 6 is a section of one of the bone fibres isolated, exhibiting very well its interior 
structure. 
Fig. 7 represents a cartilage cell, highly magnified, taken from the more superficial 
part of the articular cartilage of the head of the tibia, and which, I think, is in an early 
stage of its development. 
Fig. 8 represents a cartilage cell, from the same position as that of the preceding 
figure, and exhibiting an advance in development and the formation of a nucleus. 
PLATE 11. 
Fig. 1. A section of the more superficial part of the articular cartilage of the head 
of the os humeri, parallel with the surface, very highly magnified and exhibiting the 
flattened cell groups, apparently of later formation than those more deeply situated. 
Fig. 2. Two cell groups from the same position as figure 1 ; the right hand group, a, is 
viewed upon the surface parallel with that of the articular cartilage, and the other, b, is 
viewed upon the edge or side. 18 
Leidy, Intimate Structure, etc. of Articular Cartilages. 
Fig. 3. A vertical section of the free surface cartilage, from the articular cartilage of 
the head of the os humeri, very highly magnified, and representing the cell groups 
viewed upon their edges. 
Fig. 4 represents the escape of the mass of granular contents, held together by a 
protoplasmoid envelop, of a cartilage cell in which the wall has apparently become 
blended with the cartilage matrix, highly magnified, from the surface of the articular 
cartilage of the head of the os humeri. 
Fig. 5. A fragment of surface cartilage from the epiphyso-cartilaginous condyles of 
the os femoris of a foetus of six months, highly magnified, and exhibiting the uniform 
diffusion of the cartilage cells. 
Figs. 6, 7, 8, 9, 10, 11, 12, 13, exhibit the progress of development of the cell groups 
of perfected articular cartilages from the primitive cartilage cells. 6 is from the same 
foetus as that of figure 5. The others are from a foetus at term, a body of six years of 
age, and an adult.