BRAIN OF RABBIT 



799 



The optic lobes are fourfold— corpora quadrigemina. They are in 

 large part covered bv the cerebrum. Between them runs the iter con- 

 necting the third ventricle and the fourth. The floor of this passage is 

 formed by the thick crura cerebri which connect the medulla with the 



cerebrum. 



The cerebellum has a median and two lateral lobes (with accessory 

 floccuh), and is marked bv numerous folds, mostly transverse. The 

 two sides are connected ventrally by the pons Varolii, lymg across the 

 anterior ventral surface of the medulla. 



The medulla oblongata lies beneath and behind the cerebellum, and 



OLF 

 Fig. 480. 



BG- O.N 



-Median vertical section through Mammal's brain. 



■After Edinger. 



P4L., PaUium or cerebral cortex; CBR., cerebrum with its con- 

 volutions ; E., epiphysis, rising from the roof of the optic thalami 

 region • C.P., choroid plexus, the non-nervous roof of the same 

 region '; O.L., optic lobe ; CBL., cerebellum ; M.O., meduUa 

 oblongata ; PO., pons, the floor of the cerebellar region ; H., 

 pituitary body, borne on the hypophysis, a downgrowth from the 

 optic thalami region ; O.N., optic nerve cut short ; B.G., basal 

 ganglia of the cerebral region ; OLF., olfactory nerve ; S.C., 

 spinal cord. 



is continued into the spinal cord. The cayity of the fourth ventricle is 

 roofed by a thin membrane or velum, above which lies the cerebellum. 

 On the ventral surface the medulla is marked by a deep fissure, bordered 

 by two narrow bands or ventral pyramids. 



The spinal cord presents its usual appearance, with its dorsal sensory 

 nerve-roots with ganglia, its ventral motor nerve-roots apparently with- 

 out ganglia, and the spinal nerves formed from the union of these. The 

 gangha of the adjacent sympathetic system perhaps belong to the 

 ventral roots of the spinal nerves. 



A large number of nerves pass down the neck. Of these the following 

 are most important : — 



