NERVES 141 



4th ventricle in the expansion of pia mater across the roof. 

 There are two other openings through the pia mater, placed 

 one on each side of the upper roots of the glosso-pharyngeal 

 nerve, under the flocculus. 



THE NERVES. 



THE NERVES OF THE HEAD AND NECK. 



THE CRANIAL NERVES, 12 pairs. 



IST or OLFACTORY. Course: the olfactory tract passes 

 forwards on the under surface of the frontal lobe near the 

 longitudinal fissure, resting on cribriform plate and expanding 

 anteriorly into olfactory bulb. There is an enlargement at the 

 posterior part of the upper surface called the olfactory tubercle. 



Distribution. About twenty nerve filaments are given off 

 from under surface of the olfactory bulb (p. 134), and pass 

 downwards through ethmoidal foramina; they are divided 

 into three sets to supply Schneiderian membrane of the nose ; 

 inner to septum, middle to roof of nose, outer to superior and 

 middle turbinate bones. 



Special function. Smelling. 



2ND or OPTIC. Origin, from optic tract, which arises by two 

 roots : Outer, from external geniculate body, optic thalamus 

 and brachium of superior quadrigeminal body. Inner, from 

 internal geniculate body. 



Course. Winds across outer and anterior surfaces of crus 

 cerebri, uniting with fellow to form optic commissure, which 

 is bounded in front by the lamina cinerea and behind by the 

 tuber cmereum ; the nerves separate at fore part of commis- 

 sure, get ensheathed in arachnoid, and pass into orbit through 

 optic foramen above and internal to ophthalmic artery ; whilst 

 passing through, each receives a tube of dura mater, which 

 divides into two, the outer piece becoming orbital periosteum, 

 and the inner, ensheathing the nerve, joins the sclerotic 

 in front. The nerve pierces sclerotic and choroid coats of 

 eyeball. 



Distribution. Expands to form innermost layer of retina. 



Special function. Nerve of sight. 



3RD or MOTOR OCULI. Superficial origin : inner side of crus 

 cerebri, just in front of pons. Deep origin : floor of aqueduct 

 of Sylvius. 



Course. Pierces dura mater to enter canal in outer wall of 



