THE ALIMENTARY CANAL 289 



shaped bag, having seven openings leading into it : two 

 from the nostrils, and two from the ears ; one from the 

 windpipe, guarded by the epiglottis ; one from the mouth, 

 with a fleshy curtain called the soft palate ; and one from 

 the esophagus. It is the natural passage for food be- 

 tween the mouth and the esophagus, and of air between 

 the nostrils and windpipe. Like the mouth, it is lined 

 with a soft mucous membrane. 



The esophagus is a long and narrow tube, formed of 

 two muscular layers : in the outer layer, the fibers run 

 lengthwise ; in the other, they are circular. It is lined 



FIG. 250. Ideal Section of a Mammalian Vertebrate: A, pectoral, or fore limb; B, 

 pelvic, or hind limb; a, mouth; b, cerebrum; c, cerebellum; d, nose; e, eye; f t 

 ear; g, esophagus; h, stomach; i, intestine; /, diaphragm, or midriff; k, rectum, 

 or termination of intestine; /, anus; m, liver; , spleen; o, kidney; /, sympathetic 

 system of nerves; q, pancreas; r, urinary bladder; s, spinal cord; u, ureter; v, 

 vertebral column; -w, heart; x, lung; y, trachea, or windpipe; z, epiglottis. 



with mucous membrane. While in all fishes, reptiles, 

 and birds the body cavity is one, in mammals it is 

 divided, by a partition called the diaphragm, into two 

 cavities, the thorax, containing the heart, lungs, etc. ; 

 and the abdomen, containing the stomach, intestines, etc. 

 The esophagus passes through a slit in the diaphragm, 

 and almost immediately expands into the stomach. 



In the majority of mammals, the stomach is a muscu- 

 lar bag of an irregular oval shape, lying obliquely across 

 the abdomen. In the flesh eaters, whose food is easy 

 DODGE'S GEN. ZOOL. 19 



