THE DIGESTIVE APPARATUS IN MAMMALIA. 



The borders, in joining each other in front, describe a parabolic curve which is 

 in contact with the incisive arches. 



Structure. — The tongue offers for study, in regard to its structure : 1. The 

 mucous membrane enveloping the organ. 2. The muscular tissue which, in 

 reality, forms its mass. 3. The vessels and Jierves distributed to it. 



1. Mucous membrane. — This membrane — a continuation of that lining the 

 mouth — is reflected at the bottom of the canal on the sides of the tongue, covers 

 the upper surface of the organ, and envelops the whole of its free portion. 

 Its dermis, or corium, has not the same thickness throughout, but is incom- 

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

 inferior plane of the free part ; on the dorsum 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 glands. 



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



Fig. 216. 



Fig. 217. 



COMPOSITE PAPILLA FROM THE TONGUE 

 OF THE DOG. 



1, Corium ; 2, epithelium. 



SIMPLE FILIFORM PAPILLA FROM THE 

 POINT OF THE HOKSE'S TONGUE. 



1, Corium ; 2, epithelium. 



prolongations or papillce, which, accordmg to their shape, are distinguished as 

 filiform, fungiform, and calijciform papillce. 



The filiform papillce (Fig. 217) are formed by thin prolongations terminating in 

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

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

 longations, much smaller, and provided also with an epithelial covering. These 

 filiform papillfe 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 embedded 

 in epithelium, and are scarcely apparent in the minute elevations on its surface. 



The fungiform pcqnllcB (p. capitatce) (Fig. 219, 2) 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 papillifi. 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 papillcB (fossuJate, circumvallate, or Jetiticular pa^nllce) (Fig. 219) 

 are really f imgif orm, but instead of projecting above the free surface of the dermis, 

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

 slightly elevated ring, within which is a narrow fossa around the pedicle of the 

 papilla ; several papiUae may be contained within one cup-shaped cavity. They 



