648 TEXTBOOK OF ZOOLOGY 



of the tongiie and palate, which provides the opening from mouth 

 to pharynx, is known as the fauces. Ducts from the salivai-y glands 

 open into the mouth (Fig. 349). 



The pharynx receives the two openings of the internal nares from 

 above the hard palate and the two Eustachian tubes from the middle 

 ears. In the floor of the pharynx is the glottis which opens to the 

 respiratory tract and is guarded by the cartilaginous, flaplike epi- 

 glottis. Posteriorly the pharynx leads to the aperture of the esopha- 

 gus which is a narrow, muscular tube leading posteriorly to the 

 stomach, which lies caudal to the diaphragm on the left side. The 

 esophageal end of the stomach is known as the cardiac portion, and 

 the intestinal end is the pyloric portion. Inside, the gastric glands 

 are embedded in the fine foldings of the internal epithelium. At the 

 posterior end is a circular fold of the epithelium, embraced by a 

 sphincter muscle which serves as a valve to open and close the pylorus 

 or gateway to the intestine. Following the stomach is the small 

 intestine which is seven or eight feet long and is divided into the 

 anterior curved duodenum, the jejunum and the much-coiled ileum. 

 The duodenum receives the pancreatic duct from the pancreas and 

 the tile duct from the liver. The small intestine leads into the 

 ascending portion of the colon, which turns transversely across the 

 abdomen and follows posteriorly as the descending colon to the 

 rectum. At the anterior end of the colon is a short, blind sac extend- 

 ing beyond the point of entrance of the ileum ; this is the cecum. In 

 human beings a narrowed extension of this is the vermiform ap- 

 pendix. In the rabbit the cecum is about twenty inches in length. 

 Carnivorous animals usually have a reduced cecum. 



Circulatory System 



This system includes both the blood vascular portion and the 

 lymphatic system. The blood system is responsible for the transpor- 

 tation of oxygen, food, and excretions. The lymph of the lymphatic 

 system can be compared to blood without red corpuscles. It makes 

 intimate contact with the tissues. The plasma of the blood seeps 

 through the capillaries and is collected as Ijonph in the lymph spaces 

 of the tissues over the body. These spaces are joined by vessels and 

 many of them empty into the thoracic lymph duct which leads into 

 the large subclavian vein of the thorax. 



