336 



COMPARATIVE PHYSIOLOGY. 



ComparatiTe. — That swallowing is independent of gravity is 

 evident from the fact that long-necked animals (horse, giraffe) 

 CEin and do usually swallow with the head and neck down, so 

 that the fluid is rolled up an inclined plane. The peristaltic 

 nature of the contractions of the gullet can also he well seen in 

 such animals. In the frog the gullet, as well as the mouth, is 

 lined with ciliated epithelium, so that in a recently killed ani- 

 i mal one may watch a slice of moistened cork disappear from the 

 i mouth, to be found shortly afterward in the stomach. The rate 

 of the descent is surprising — in fact, the movement is plainly 

 visible to the unaided eye. 



The Movements of the Stomach.— The stomach of mammals, 

 including ma,n, is provided with three layers of muscular fibers ; 

 1. External longitudinal, a continuation of those of the oesopha- 

 gus. 2. Middle circular. 3, Internal oblique. The latter are 

 the least perfect, viewed as an investing coat. The pyloric end 

 of the stomach is best supplied with muscles ; where also there 

 is a thick muscular ring or sphincter, as compared with which 

 the cardiac sphincter is weak and ill-developed. 



Pig. 875. 



Fig. 876. 



Fig. 875.— Muscular fibers of the stomach of horse; external and middle layers (Chau- 

 veau). A, fibers of external layer enveloping left sac; B, fibers of middle plane 

 in right sac; C, fibers of oesophagus. 



Fig. 376. — I)eep and muscular layers exposed by removing mucous membrane from an 

 everted stomach (Chauveau). A, deep layer of fibers enveloping left sac; B, fibers 

 of middle plane which alone form the muscular layer of right sac; C, fibers of 

 oesophagus. 



The movements of the stomach begin shortly after a meal 

 has been taken, and, as shown by observations on St. Martin, 

 continue for hours, not constantly, but periodically. The effect 



