642 



BIRDS. 



it- 



glandular part of the stomach (the proventriculus), where 

 gastric juice is secreted from large glands. 



Beneath the proventriculus is the gizzard, in which the 

 food is ground. The walls are very muscular, the fibres 

 radiating from two tendinous discs ; the internal surface is 

 lined by a hard horny epithelium ; and within the cavity are 

 small stones which the bird has swallowed. In hawks and 

 fish-eating birds the gizzard region is, naturally enough, 

 fairly soft. The pyloric opening, from the gizzard into the 

 duodenum, is very near the cardiac opening from the 

 proventriculus into the gizzard. 



In the fold of the long duodenum 

 lies the pancreas with three ducts, 

 whose number points to the triple 

 origin of the pancreatic rudiment in 

 the embryo. Into the same region 

 open two bile ducts from the two- 

 lobed liver, which is without a gall- 

 bladder in the common pigeon, though 

 this is present in some birds, and even 

 in some species of pigeon. 



The small intestine is long ; the 

 large intestine is very short ; in fact, 

 it is not more than a rectum two 

 inches in length. At the junction of 

 the small and the large intestine there 

 are two short caeca. In some birds, 

 e.g. the fowl, these are of considerable 

 length ; in the ostrich they are very long ; 

 in the hornbills, etc., they are absent. 

 The cloaca has three divisions (see Fig. 319), an upper 

 part into which the rectum opens, a median part into which 

 the ureters and the genital ducts open, and a posterior region 

 (proctod?eum), opening into which from the dorsal surface 

 is a vascular and glandular sac of obscure function, the 

 bursa Fabricii, which usually disappears during adolescence. 

 Vascular system. The relatively large four-chambered 

 heart, the complete separation of arterial and venous blood, 

 the single aortic arch bending over to the right side, and 

 the hot blood (about 38 C, 100 F.), are important 

 characteristics. The heart beats are more rapid in birds 



FIG. 319. Diagram- 

 matic section of clo- 

 aca of male bird. 

 After Gadow. 



cd., Upper region of clo- 

 aca into which rectum 

 opens ; nd. , median re- 

 gion into which ureter 

 (it.) and vas deferens 

 (ev/.) open from each 

 side ; pd. , posterior re- 

 gion into which bursa 

 Fabricii (Z?. /*".) opens. 



