98 



A COURSE ON ZOOLOGY. 



differences from the corresponding organs of man and 

 the dog. 



The digestive apparatus has really three stomachs : 

 1st, the craw, or first stomach, which is only an en- 

 largement of the lower end of the oesophagus; the 

 food accumulates in this reservoir so as to make it pro- 

 trude in front of the neck, but the aliments do not here 

 undergo any elaboration ; 2d, the succenturial ventricle, 

 or second stomach, which has thick, glandular walls that 

 secrete a fluid to moisten the food ; 3d, the gizzard, or 

 third stomach, formed of thick, muscular walls lined 

 interiorly with a ha* d, horny epithelium. The succentu- 

 rial ventricle repre- 

 sents the stomach of 

 the dog, but the giz- 

 zard is an apparatus 

 of trituration, and is 

 consequently large- 

 ly developed in all 

 graminivorous birds. 

 The caecum is repre- 



FIG. 53. 



sented by two tubes, 

 the terminal orifice 

 of the intestine be- 

 ing also that of the 

 urinary ducts, and 

 forming what is 

 called the cloaca. 



The respiratory 

 apparatus differs 

 sensibly from that 

 of the dog. The 

 bronchi, instead of being entirely distributed to the lungs, 



LUNGS OF BIRD. a, base of trachea ; 6, 5, bron- 

 chial tubes ; c, branches of bronchi ; d, blood- 



