NERVOUS SYSTEM 57 



4. The Corpus Callosum is the broad white band 

 of fibres connecting the two cerebral hemispheres. 

 It may be seen from the dorsal side by pressing 

 the hemispheres apart. (Plate VII., c.) 



5. The Corpora Quadrigemina are the two pairs of 

 rounded elevations which lie on the dorsal surface 

 of the brain, between the cerebrum and cerebellum, 

 which must be pressed apart to expose them. The 

 anterior pair are smaller than the posterior, and 

 are called the nates. The posterior pair are called 

 the testes. (Plate VII., c.) 



6. The Pineal Gland is a single rounded promi- 

 nence, lying in the mid-dorsal line, just anterior to 

 the nates. (Plate VII., c.) 



7. The Valve of Vieussens is the delicate mem- 

 brane covering the cavity of the brain, posterior to 

 the corpora quadrigemina and beneath the anterior 

 portion of the cerebellum. (Plate VII., c.) 



8. The second pair of cranial nerves, the Optic, 

 are the large nerves arising from the transverse 

 band of fibres known as the optic chiasma, situ- 

 ated on the ventral side of the brain, just posterior 

 to the fissure separating the two hemispheres. 

 (Plate VII., A and c.) 



9. The Optic Chiasma is formed by the crossing 

 of the fibres of the optic tracts which run up be- 

 neath the cerebral lobes and over the ventral sur- 

 face of two oval bodies, the optic thalami, to 

 which they send fibres, and end finally in the cor- 

 pora quadrigemina. (Plate VII., A and c.) 



