THE PIGEON. 



255 



diameter, and at the junction of the two there is a strong 

 ventral flexure : it is marked ventrally with a median longi- 

 tudinal groove, separating the ventral pyramids : on the 

 upper side are the dorsal pyramids, which, passing from 

 behind forwards, diverge, leaving a median dorsal hollow, 

 the fourth ventricle (Fig. 59, v.^). 



A 



B 



cJi 



O.I 



FIG. 58. Columba livia. The brain. A, from above ; B, from 

 beneath ; C, from the left side ( x 2). 



cb, cerebellum : c.h, cerebral hemispheres : f, flocculus : inf, infun- 

 dibulum : m.o, medulla oblongata : o.l, optic lobes : olf, olfactory lobes : 

 o.t, optic tracts : pn, pineal body : H-XII, roots of cerebral nerves : 

 sp.l t root of first spinal nerve. 



