336 THE DIGESTIVE APPARATUS IN MAMMALIA. 



parably thinner and less dense on the sides of the fixed portion and the 

 inferior plane of the free part ; on the dorsuin of the tongue it is difficult to 

 cut it. Its deep face receives the insertion of a large number of the muscular 

 fibres of the organ, and for the greater part of its extent it adheres in the 

 most intimate manner to these fibres ; though its adherence is not so close 

 at those points where it is in contact with the labial glandules. 



Its superficial face is not smooth, but shows a prodigious quantity of 

 minute prolongations or papillae, which, according to their shape, are dis- 

 tinguished as filiform, fungiform, and calyciform papillce. 



The filiform papillce are formed by thin prolongations terminating in a 

 point, each being covered by an epithelial sheath which greatly increases its 

 dimensions. They are simple or composite, having at their summit 

 secondary prolongations, much smaller, and provided also with an epithelial 

 covering. These filiform papillae are largest on the middle part of the 

 dorsum of the tongue, where they present a tufty appearance ; towards the 

 point of the organ they are imbedded in epithelium, and are scarcely 

 apparent in the minute elevations on its surface. 



The fungiform papillce (p. capitatce) are club or sponge-shaped elevations 

 of the derm, attached to the membrane by a short pedicle. Their surface is 

 convex and smooth, or studded with filiform papillae. They are scattered 

 irregularly over the dorsum of the tongue, among the filiform papillae, and 

 are most numerous on the posterior third of its surface. 



The calyciform papillce (fossulate, circumvallate, or lenticular papillae) are 

 really fungiform, but instead of projecting above the free surface of the derm, 

 they are placed in a depression of this membrane. They are surrounded 

 by a slightly-elevated ring, within which is a narrow fossa around the 

 pedicle of the papilla ; several papillae may be contained within one cup- 

 shaped cavity. They only exist at the base of the tongue, where two of 

 their number, very developed and composite, correspond to the blind holes of 

 Morgagni (foramen ccecum). At the base of a certain number of the fungi- 

 form and calyciform papillae is a band of adenoid tissue. 



It is generally believed that these three kinds of papillae have each a 

 distinct function ; the filiform are to retain the alimentary and sapid sub- 

 stances on the surface of the tongue ; the fungiform are tactile organs, and 

 the calyciform are gustatory. 



2. Muscles. Beneath the mucous membrane, on the dorsal surface of 

 the tongue, is a cylindrical fibrous cord which sometimes attains the thick- 

 ness of a large goose-quill. This cord is situated in the median plane, 

 near the middle part of the organ, and is from 2 to 3 inches loog. It may 

 be considered as a fibrous support to the muscular tissue, and it sometimes 

 directly adheres to the deep surface of the tegument. At other times, it is 

 only connected with that membrane by a very short lamellar prolonga- 

 tion, and is then buried a little deeper among the fibres of the superior 

 muscular layer. 



(The German hippotomists designate this the cartilage of the tongue. It 

 is only found in Solipeds, and was first described by Briihl, who gave it this 

 designation. Leyh states that it is composed of dense fibro-cartilage, 

 surrounded by cellular and adipose tissue ; that it is from 4 to 7 inches 

 long, and f ths to 1 inch in thickness ; and that it commences about an inch 

 from the anterior appendix of the hyoid bone.) 



A similar cord, but not so strong or well defined, is sometimes found at 

 the inferior surface of the free portion of the tongue. 



Intrinsic muscles. In studying the proper substance of the tongue ia 



