20 



THE RIDDLE OF MIGRATION 



entire spinal cord is now dominated by and under 

 direct control of the cortical centres. Moreover, 

 the mammalian brain possesses, in the corpus cal- 

 losum, a huge sheet of transversely running fibres 



Fig. 2. Brain of Cat and of Crow 



A: Brain of cat: dorsal aspect. B: brain of crow: dorsal 

 aspect. B^: same, ventral aspect. Cb, cerebellum; Hm, cerebral 

 hemisphere; Md, medulla; 01, olfactory lobe; Op, optic lobe. 

 (Scale of B and B^ slightly greater than A .) 



that puts the two hemispheres into the most inti- 

 mate relationship with each other. Even the cere- 

 bellum, already an important correlation centre in 

 fishes, is now supplied with a new and additional 



