XII 



PHYLUM CHORDATA 



479 



capillaries. This is perhaps the most important physiologi- 

 cal advance made by birds over reptiles. 



The aortic arch curves over the right bronchus to reach 

 the dorsal body-wall, and then passes directly backwards as 

 the dorsal aorta. 



olf 



B 



cJt 



If 



o.t 



FIG 289. - Columba livia. The brain; A, from above; B, from below; C, from 

 the left side, cb, cerebellum; c. h, cerebral hemispheres; f, flocculus; t'ttf, in- 

 fundibulum; in. o, medulla oblongata; o. I, optic lobes; o. t, optic tracts; pn, 

 pineal body; II-XIII, cerebral nerves; sp. I, first spinal nerve. (From Parker's 

 Zootomy.) 



The brain completely fills the cranial cavity, and is re- 

 markable for its short, broad, rounded form. The cerebellum 



