OL.L 



OP.L 



CBL 



SC 



C6L 



SC 



OL.L 



N 



ON 



CB 



MO OPL PIT 



FIG. 43. THE BRAIN OF A PIGEON, FROM ABOVE AND FROM THE SIDE. 



OL.L, small olfactory lobes ; CB, large smooth cerebral hemispheres 

 or fore-brain ; P.B, the pineal body rising from the roof of the second 

 part of the brain, the optic thalami ; OP.L, optic lobes (the third part of 

 the brain) which are thrust to the side in the course of development in 

 birds by the preponderant growth of the cerebral hemispheres (CB) and the 

 cerebellum (CBL) ; PIT, the pituitary body, a downgrowth from the 

 region of the optic thalami which at an early stage in development meets 

 an upgrowth from the roof of the mouth cavity and fuses with it ; it is 

 in part an organ of internal secretion. The fourth part of the brain is the 

 cerebellum (CBL) ; the fifth part is the medulla oblongata (MO), from 

 which most of the cranial nerves (N) arise ; it is continued into the spinal 

 cord (S.C). The optic nerves (O.N), seen far forward on the side view, 

 arise from the optic thalami and have some of their fibres passing into the 

 optic lobes. 



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