222 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



PHARYNX. 



The pharynx is the division of the alimentary canal intervening 

 between the cavity of the mouth and the oesophagus and is characterized 

 by being at once alimentary and respiratory. From its walls are devel- 

 oped the gill clefts and lungs as well as a number of derivatives of 

 these, and it also receives the internal openings of the nasal passages. 

 Hence it is best described in connection with the respiratory system. 



FIG. 226. Salivary glands of fruit bat, Pteropus conspicillatus (Princeton, 2065). 

 p, pd, parotid gland and duct; rl, rid, retrolingual gland and duct; sm, smd, submaxillary 

 gland and duct. 



THE (ESOPHAGUS. 



That part of the digestive tract between the pharynx and the 

 entrance of the bile duct (fig. 209) develops into oesophagus, stomach 

 and that part of the intestine known as the duodenum. Stomach and 

 duodenum are separated by the pyloric valve described below, but it 

 is difficult to draw a clear line between oesophagus and stomach. In 

 general it may be said that the oesophagus is the tract immediately 

 succeeding the pharynx, lying in front of the body cavity and thus 

 lacking a serous coat; that it is smaller than the stomach, and that 

 there are no digestive glands in its walls; but all of these statements 

 have exceptions. 



