XL] THE A LIMENTAR Y S YS TEM. 44 1 



in the Rabbit and Proteles ; or but one, as in the Rat and 

 Pig. They may be disposed in two parallel lines, as in the 

 Sheep ; or altogether absent, as in the Manatee. They may 

 be, as in the Orang, arranged in the same way that they are 

 in Man ; or they may form the letter Y or T, as in the 

 Chimpanzee. There may be a large horny papilla on each 

 side, as in Manatee and Ornithorhynchus ; or there may be 

 horny plates on the tongue, as in the Java Porcupine. 



The tongue may be extraordinarily smooth, but with little 

 mobility and flexibility, as in the Elephant ; or small, nar- 

 row, and tied down, as in the Manatee. It may have a bi- 

 furcating apex, as in the Seal. It may be enormous, yet 

 attached all round nearly to the very tip, and without 

 papillae, as in the Whalebone Whale. 



The tongue may be exceedingly long, and furnished all 

 round, except at the tip, with backwardly pointing spines, as 

 in the Tamandua. 



This organ attains its greatest relative length amongst 

 Mammals in Mcinis, where its muscles extend backwards, 

 taking origin in the very elongated xiphoid process of the 

 sternum. There is also a sterno-glossal muscle in the Great 

 Ant-eater and in the Echidna. 



There may be a considerable cartilaginous lamelliform 

 process extending forwards beneath the tongue, taking 

 origin from its under surface further back, and having the 

 appearance of a second small tongue beneath the true one. 

 Such a structure is found in Lemurs. It is independent of 

 the papillae for the sub-maxillary ducts, which papillae are at 

 the same time conspicuous. 



These latter may unite to form a little bifid body beneath 

 the tongue, as in the Gibbons. 



The papillas on which the sub-maxillary ducts open may 

 be more elongated than in man : such is the case even in the 

 Chimpanzee. 



8. The (ESOPHAGUS, or gullet, of man is a nearly straight 

 membranous and muscular tube, leading from the phaiynx 

 to the stomach. 



It consists externally of longitudinal and also of circular 

 muscular fibres. Within this muscular coat there is cellular 

 tissue, and this again is lined with mucous membrane. 



The STOMACH is formed of similar materials, and has been 

 sufficiently described in the Sixth Lesson of " Elementary 

 Physiology," 18. It is a simple, somewhat pear-shaped 

 bag, curved, so that its upper surface is concave. The gullet 



