VERTEBRATA. 



from the first or first and second visceral arches. In some 

 it is without powers of motion, but frequently it is very 

 mobile. Usually it is attached behind, the front margin 

 being free, but in many batrachia it is attached in front 

 and folded back in the mouth. 



The mouth-cavity is succeeded by the pharynx, a region 

 distinguished by containing the respiratory openings (inter- 

 nal nostrils, gill-slits, glottis, p. 93). 



Behind the pharyngeal region is the digestive tract proper. 

 In some vertebrates it is scarcely possible to distinguish 



FIG. 66. Diagram of the digestive tract of a mammal, if), brain ; d, 

 diaphragm ; ft, heart ; i, intestine ; fr, kidney ; i, liver ; o, oasophagus ; 

 p, pancreas ; s, stomach ; sp, spleen ; v, vent. 



regions in it, but in most cases several distinct portions 

 occur. Those usually to be recognized are the following: 



The pharynx communicates with the gullet or oesopha- 

 gus, a muscular tube which frequently serves only to carry 

 food back to the stomach. On the other hand, a part of this 

 tube may be expanded into a glandular food-reservoir or 

 crop (birds). 



In some fishes and batrachia the stomach is hardly differ- 

 entiated from the oesophagus, but in other forms it is well 

 developed, with muscular and glandular walls. It may 

 even be divided into several portions. Thus in birds (Fig. 



