THE ALIMENTARY CANAL. 



247 



On 



K 



salivary glands. There is no velum palati. The muscular, longi- 

 tudinally folded oesophagus, the length of which in general depends 

 on that of the neck, frequently possesses especially in the birds of 

 prey, but also in the larger granivorous birds (Pigeons, Fowls, 

 Parrots) a crop-like dilatation, in which the food is softened (fig. 056). 

 In the Pigeons the crop bears two 

 small round accessory sacs, the walls 

 of which secrete in the breeding- 

 season a cheesy substance used in 

 feeding the young. 



The lower end of the oesophagus 

 is dilated into a glandular pro- 

 ventriculus, which is followed by 

 the wide muscular stomach (gizzard}. 

 While the proventriculus has, as a 

 rule, an. oval form and is smaller 

 than the gizzard, the latter is pro- 

 vided with muscular walls, which are 

 weaker (birds of prey) or stronger 

 (granivorous birds), according to the 

 kind of food eaten. In the grani- 

 vorous birds the gizzard is excellently 

 adapted for the mechanical prepara- 

 tion of the softened food material 

 by the possession of two solid plates, 

 which form the horny internal wall, 

 and work against one another. The 

 tirs-t loop of the small intestine 

 (corresponding to the duodenum) 

 surrounds the elongated pancreas, 

 the ducts of which, as well as the 

 usually double bile ducts, open in 

 this region. The beginning of the 

 >hort large intestine is marked by a 

 circular valve, and by the origin of 

 two ca>ca ; it presents no distinction 

 into colon and rectum, and passes into the cloaca, into which the 

 urinogenital apparatus also opens. At its entrance into the cloaca 

 it presents a sphincter-like circular fold. A peculiar glandular sac 

 the bursa Fabricii opens into the dorsal wall of the cloaca. 



The large elongated kidneys are placed in excavations of the 



FIG. 656. Digestive canal of a bird. Oc, 

 oesophagus ; K, crop ; Dm, proventricu- 

 lus ; Km, gizzard ; D, small intestine ; 

 P, pancreas (placed in the duodenal 

 loop) ; H, liver ; C, the two cca ; Ad, 

 large intestine ; U, ureter ; Ov, ovi- 

 duct; .E7, cloaca. 



