[Reprint from The 'Microscope for July. 1889.] The Microscope. Published on the 10th of Each Month, At 25 Washington Avenue, Detroit, Mich, All articles for publication, books for review and exchanges should be addressed to the Editors of “ The Microscope,” 25 Washington Ave., Detroit, Mich. Subscriptions, Advertisements, and all business matters, are attended to by The Microscope Publishing Co., 25 Washington Avenue, Detroit, Mich. All remittances promptly acknowledged. To insure answer, letters of inquiry, not intended for publication, must inclose a two cent stamp. Authors of papers will be supplied with 25 reprints free, when the desire for such is stated on the manuscript. Specimens for examination should be sent to the Microscope Laboratory. 25 Washington Avenue, Detroit, Michigan. In all cases the transportation charges on these specimens must be prepaid. Vol. IX. No. 7. DETROIT, JULY, 1889. ORIGINAL COMMUNICATIONS. ON THE GUSTATORY ORGANS OF SCIURUS CARO LINENSIS. [plate VII.] FREDERICK TUCKERMAN. T N the tongue of most Rodentia the posterior portion rises some- what abruptly above the level of the anterior. The tongue of S. carolinensis possesses this characteristic, although not especially well marked. The organ is 40mm. in length, 10mm. in breadth, and 8mm. in thickness, and is perfectly free for 17mm. from the fraenum. The papillate surface is usually marked by a superficial longitudinal groove extending along the anterior half to the tip. In some specimens the groove passes directly through the apex, and from thence is continued to the fraenum. The dorsum, anterior to the area of the circumvallate papillae, is thickly beset with small, recurved papillae of mechanical function. These papillae vary in form, some being cone and others more or less cylinder-shaped. The latter measure 0.40mm. in height and 0.14mm. in breadth at their widest part, and, in the mid-dorsal region of the tongue, are about 0.35mm. apart. They are more or less flattened on top, with perpendicular sides, and each is seated upon one or more papillary upgrowths of the mucosa. The epithelium covering the papillae is somewhat imbricated, and the spaces between them are filled to some height with epithelium likewise imbricated in arrangement. Not infrequently the papillae have one or more cornified spines projecting from their upper surface, the points of which are directed inwards 194 The Microscope. and backwards. The cone-shaped papillae investing the upper surface and sides of the anterior half of the tongue do not differ in character very materially from ordinary conical papillae. About the gustatory area and root are thick, fleshy, cone-shaped elevations, the apices of which are turned backwards. Fungiform papillae of the normal type are distributed over the upper surface and sides of the organ, attaining their maximum size in the tract directly in front of the circumvallate papillae. The circumvallate papillae are three in number and are situated well back on the dorsum. They are arranged in an isosceles triangle, the apex of the triangle being backwards. At each side of the tongue, near the base, is a papilla foliata. The inner border of these papillae is marked by a fringe of large, fleshy papillae, the apices of which are directed upwards, inwards and backwards. This fringe is continued for some distance on to the glosso-palatine arch. GUSTATORY STRUCTURES. The Circumvallate Papillae.—These papillae show no indica- tions of lobation. Their upper surface, which is somewhat uneven, overtops the surrounding lingual area. The epithelium covering their free surface measures about 0.07mm. in thickness, being a trifle thicker than that protecting the sides. The lateral walls of the papillae curve downwards and inwards, giving them a rather constricted base. The trench encircling each papilla is deep, narrow, and quite uniform in breadth. Serous glands are fairly abundant in the underlying stroma, and also occur within the papillary body itself. Their ducts open into the trench at its deeper part. Nerves of considerable size enter the papillae at their base, and their branches (which are for the most part non-medullated) radiate to the summit and lateral regions of the papillae, in the mucosa of which they cease to be longer distinguishable. The taste-bulbs of the circumvallate papillae are only fairly numerous. They are disposed at the sides in a zone of four to six tiers, the uppermost tier being about opposite the middle of the trench. I failed to detect taste-bulbs in the epithelium of the free upper surface of the papillae, and they were likewise wanting in that investing the outer wall of the trench. From horizontal sec- tions, made at different levels, I estimated the number of bulbs in a tier at fifty. If we allow for five tiers, we shall have two hundred and fifty bulbs for each of the three papillae. The bulbs present the usual amount of variation in size and shape. (Fig. 2 shows their external structure magnified 240 diameters.) The mean length of the bulbs is 0.057mm., and their mean breadth 0.032mm. Fig- 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig 6. PLATE VII. The Microscope. 195 The Papillae Foliatce.—The exposed surfaces of these papillae are somewhat flattened. Each papilla consists of five bulb-bearing folds, possessing the same general appearance, but varying some- what in size. The furrows separating the folds are quite narrow, with a nearly uniform breadth throughout, and have an average depth of about 0.5 mm The folds are for the most part simple in construction. Each one bears secondary papillae at its upper part, the depressions between which are filled by the epithelium. Serous glands and ducts are abundant, aud the latter discharge into the fur- rows at different levels. (The foliate papilla is shown in figs. 3 and 4.) The taste bulbs of this area are, as a rule, restricted to the lower two-thirds of the folds, although occasionally they completely fill the sides of a fold. They are usually arranged in eight tiers, though there may be more. Judging from horizontal sections, the number of bulbs in each lateral gustatory organ is about eleven hundred. The Fungiform Papillae.—These papillae commonly bear a single taste-bulb at their upper part. The bulb usually lies verti- cally, directly in the long axis of the papilla, with its apex penetrat- ing (but not invariably perforating) the outer homogeneous layers of stratified pavement epithelium, and its base resting in a depres- sion of the mucosa. The bulbs of this region are somewhat pyri- form in shape, and measure 0.051 mm. in length, their greatest transverse diameter being 0.025 mm. At the lower part of the posterior surface of the epiglottis I found a few isolated bulbs embedded in the stratified epithelium. The apices of these bulbs fail to pierce the superficial strata of the epithelium, and their bases but rarely touch the mucosa. They measure from 0.039 to 0.048 mm. in length and are 0.030 mm. in breadth. Small mucous glands are very abundant in this region, and their ducts, which are numerous, quite straight and more or less parallel, perforate the epithelium and open on the posterior sur- face. No ducts were observed communicating with the anterior surface of the epiglottis. EXPLANATION OF PLATE—REFEBENCE LETTERS. 6., bulb; d. 1., deep lamina of epithelium; /, furrow; fd., fold of the papilla; f. s., free surface of the epithelium; gl., serous gland; gl. d., duct of serous gland; m., mucosa; st. m., striated muscle - fibres; s. I, superficial lamina of epithelium; s. p., secondary papillae; t., trench; t. b., taste-bulb. Fig. 1 x 40. Vertical section through one of the circumvallate papillse. 196 The Microscope. Fig. 2 x 240. Vertical section through one side of the base of the same circumvallate papilla, showing the bottom of the trench and the four lowest tiers of taste-bulbs, t. 6., Taste-bulb, the refer- ence mark indicating the apical end. Fig. 3 x 40. Transverse vertical section through one of the papillae foliatae. Fig. 4 x 40. Horizontal section through the upper part of one of the papillae foliatae. st. m., Striated muscle-fibres which have been divided transversely to their long axis. Fig. 5 x 240. Vertical section through a fungiform papilla of the mid-dorsal region of the tongue, showing a single taste-bulb at its upper part. The two upper thirds of the bulb are embedded in the epithelium and the lower third rests in a depression of the mucosa. Fig. 6 x 240. Transverse vertical section through the lower part of the posterior surface of the epiglottis. 6., Bulb-like struc- ture, entirely epithelial in position. Amherst, Mass.