Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 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
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 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, giz
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