DIGESTIVE APPARATUS. 



723 



Fig. 358. 



(2048.) In most birds, in consequence of the very small size of the 

 cavity of the stomach, or gizzard, as it is generally called, some other 

 receptacle for the aliment becomes indispensable; and accordingly 

 various provisions have been made for lodging food in sufficient quan- 

 tities in situations where it may be retained until the gizzard is ready 

 to receive it. In birds that catch insects on the wing, this is most con- 

 veniently effected by dilating the fauces and upper part of the throat 

 into a capacious chamber, wherein the insects as they are seized accu- 

 mulate : this is remarkably the case in the Swifts. In the Pelican a 

 very peculiar plan is adopted : the beak is amazingly prolonged, and be- 

 neath the lower jaw is suspended a white pouch, formed by the skin of 

 the throat, wherein large quantities of fish may be contained and carried 

 about. In other fishing birds the whole oesophagus is extraordinarily 

 capacious, and will hold a considerable supply ; but the most usual ar- 

 rangement in birds requiring 

 such a reservoir is the exist- 

 ence of a crop, or dilatation of 

 some part of the gullet into a 

 wide bag (inyluvies), where- 

 in grain or other substances 

 hastily picked up maybe stored 

 preparatory to digestion. After 

 expanding into the crop in 

 those birds that possess this 

 cavity, the oesophagus again 

 contracts to its former dimen- 

 sions (fig. 358, a) ; but just - 

 before terminating in the giz- 

 zard, it again dilates to form a 

 second but smaller cavity (>), 

 called the proventriculus, or 

 bulbus glandulosus, in which 

 the food undergoes further 

 preparation. The walls of 

 the proventriculus are thickly 

 studded with large glandular 

 follicles, variously disposed, from whence a copious secretion of "gastric 

 juice," as it is called, is poured out and mixed with the aliment. Having, 

 therefore, undergone maceration in the juices of the crop, and become 

 subsequently saturated with the gastric fluid, that constitutes so import- 

 ant an agent in digestion, alimentary substances are at length received 

 into the gizzard (c), where further preparation is necessary. 



(2049.) The gizzard in such birds as feed upon vegetable substances 

 is an organ possessing immense strength, and constitutes, in fact, a 

 crushing mill, wherein nutritive materials are bruised and triturated. 



3A2 



Gizzard of a bird. 



