ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 425 



The continuation of the third ventricle down into the 

 infundibulum is now apparent. Running across the third 

 ventricle from one side to the other may be seen several 

 commissures serving to connect the sides. The attachment 

 of the pineal gland to the optic thalami is now also evident. 

 From the blood-vessels which supply the brain several 

 arterial branches reach the third ventricle and are from the 

 third ventricle carried through the foramina of Monro into 

 the lateral ventricles, where as the choroid plexus of the 

 brain they line the walls of these ventricles more or less 

 completely and serve to nourish them. It not infrequently 

 happens that these delicate blood-vessels are injured and a 

 hemorrhage of the brain occurs, inducing apoplexy. 



If an incision should be made through the corpus stria- 

 turn it would be seen to be divided in its posterior region 

 into an inner and outer portion by a band of white nerve 

 fibers. This band is called the internal capsule and consists 

 of a large number of nerve fibers which are on their way 

 from the surface of the cerebral hemisphere to the cord. 



The Cranial Nerves. 



Twelve pairs of nerves arise from the base of the brain, 

 the names of which in their successive order and the distri- 

 bution of which are as follows: 



First. The olfactory nerve passing through the cribri- 

 form plate of the ethmoid and innervating the membrane of 

 the nose. It is the nerve of smell. It differs materially 

 from other nerves in that the fibers are not wrapped up into 

 definite nerve trunks by a connective tissue epineurium. 



Second. The optic nerves leading to the eye and spread- 

 ing out there in the retina. They are wholly sensory, carry- 

 ing the visual sensations to the brain. 



Third. The motores occult. These arise from the crura 

 cerebri and are distributed to the muscles of the eye, ex- 

 cluding, however, the external rectus and superior oblique. 

 They are motor nerves and control the movements of the 

 eye which these muscles produce. In addition to that, fibers 



