174 



ANIMAL PHYSIOLOGY. 



[LESSON 49. 



FIG. 279. 



Vultures, Hawks and Owls, and other rapacious birds, are strong, 

 short, compressed, arched, curved at the point, dense in their tex- 

 ture, and with sharp, cutting edges, to seize, and tear, and cut the 

 flesh of living prey. In fine, the external forms of the mouth cor- 

 respond with and indicate the structure of the internal organs of di- 

 gestion, and afford useful characters for the division of the class. 



Want of space, however, will 

 not permit more than two il- 

 lustrations of the digestive or- 

 gans, and the birds selected 

 for this purpose are the com- 

 mon Fowl and the Crow. 



761. The length of the nu- 

 trimental canal differs great- 

 ly in the several orders of 

 Birds ; it obeys the common 

 law of being shorter in the 

 flesh-consuming tribes, and 

 of greater length in those 

 feeding on a vegetable diet. 

 In nearly all the members 

 of this class, the food is de- 

 tained in a preliminary sac, 

 formed by the dilatation of 

 some part of the mouth, 

 pharynx, or oesophagus, be- 

 fore it passes into the sto- 

 mach, and in this receptacle 

 it frequently undergoes a 

 partial state of digestion. 

 In most of the small birds, 

 feeding upon grain, and in 

 the common poultry, a spe- 



Alhnentary caiial, Fowl. c ia) gac j s developed from 



the oesophagus, called the crop (6, Fig. 279). The food is allowed to 

 lie and macerate for some time in a fluid abundantly secreted by a 

 number of follicles situated in the walls of the crop, which prepares 

 it for the more perfect process of digestion, which it will receive in 

 the stomach. 



762. From the crop the oesophagus (a) continues, exhibiting 



