492 



MANUAL OF ZOOLOGY. 



into a second cavity, which is known as the " proventriculus " 

 or " ventriculus succenturiatus " (/). This is the true digestive 

 cavity, and its mucous membrane is richly supplied with gastric 

 follicles which secrete the gastric juice. The proventriculus, 

 however, corresponds, not with the whole stomach of the 

 Mammals, but only with its cardiac portion ; and it opens into 

 a second, muscular cavity, which corresponds to the pyloric 

 division of the Mammalian stomach. The gizzard (g) is situ- 

 ated below the liver, and forms in all birds an elongated sac, 

 having two apertures above, of which one conducts into the 



Fig. 215. Digestive System of the common Fowl (after Owen), o Gullet ; c Crop : 

 / Proventriculus ; g Gizzard ; sm Small intestine ; k Intestinal cseca ; / Large in- 



testine ; cl Cloaca. 



duodenum or commencement of the small intestine, whilst the 

 other communicates with the proventriculus. The two chief 

 forms of gizzard are exhibited respectively by the Raptorial 

 birds, which feed on easily - digested animal food, and the 

 Rasores and some of the Natatores, which feed on hardly- 

 digested grains. In the birds of Rapine the gizzard scarcely 

 deserves the name, being, as a rule, -nothing more than a wide 

 membranous cavity with thin walls. In the granivorous birds, 

 whose hard food requires crushing, the gizzard is enormously 

 developed ; its lining coat is formed of a thick, horny epithe- 



