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. 



"WW 



Fig. 289. — Columba livia The brain; A, from above; B, from below; C, from 

 the left side. en, cerebellum: c. h , cerebral hemispheres; _/, flocculus; inf, in- 

 fundibulum; m. 0, medulla oblongata; o. /, optic lobes; 0. t, optic tracts; /«, 

 pineal body; II-XIII, cerebral nerves; s$, 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 



