402 



TEE DIGESTIVE APPARATUS IN MAMMALIA. 



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

 in contact with the incisive arches. 



Structuee. — 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 nerves 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. 



COMPOSITK PAPILLA FROM THE TONGUE 

 OF THE DOG. 



1, Corium ; 2, epithelium. 



-1 



SIMPLE FILIFORM PAPILL.E FROM THE 

 POINT OF THK horse's TONGUE. 



1, Corium ; 2, epitiielium. 



prolongations or papUlce,, which, according to their shape, are distinguished as 

 filiform, fungiform ., and calyciform papilla!,. 



The filiform papillcB (Fig. 217) 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 pro- 

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

 filiform papillas 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 papillfB (p. capitafcc) (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 papilla3. They are 

 scattered irregularly over the dorsum of the tongue, among the filiform papilla?, 

 and are most numerous on the posterior third of its surface. 



The calyciform papilhp (foss^ilafe, circumvallate, or lenticular papilke) (Fig. 219) 

 are really fungiform, 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 papillae may be contained within one cup-shaped cavity. They 



