THE THIRD PAIR. 



529 



Surface attachment. — The nerve is attached to the inner surface 

 of the crus cerebri in the interpeduncular s]jace, immediately in front 

 of the pons. Each nerve consists of a number of funiculi which arise 

 in an oblique line from the surface. 



Deep origin. — The fibres, diverging-, pass backwards through the 

 substance of the crus, some through the locus niger, some through the 

 tegmental nucleus, to reach the grey matter in which the majority of 

 them end. This is a collection of large multipolar nerve- cells, lyiu"- on 

 each side close to the middle line, beneath the thick layer of °grey 

 matter which forms the floor of the aqueduct of Sylvius, and below 

 the corpora quadrigemina. The anterior portion"^ of the nucleus, 

 beneath the anterior of the corpora quadrigemina, is that in which 

 the fibres of the third nerve end, the posterior portion giving orio-in 

 to some of the fibres of the fourth nerve. 



A few fibres are said to run downwards in the pons, among its lono-i- 

 tudinal fibres. 



Fi£r. 333, 



Fig. 333. — View from above 

 OP THE Uppermost Nerves 

 OF THE Orbit, the Gas- 

 SERiAN Gaxglton, &c. (from 

 Sappey after Hii-sclifeld and 

 Leveille). § 



I, the olfactoi-y tract passing 

 forwards into the bulb ; H, the 

 commissure of the optic nerves ; 

 HI, the oculo-motor ; IV, the 

 trochlear nerve ; V, the gi-eater 

 root of the fifth nerve, a small 

 portion of the lesser root is 

 seen below it ; VI, the sixth 

 nerve ; VII, facial ; VIH, audi- 

 tory ; IX, glosso -pharyngeal ; 

 X, pneumo-gastric ; XI, spinal 

 accessory ; XII, hypoglossal ; 

 1, the Grasseriau ganglion; 2, 

 ophthalmic nerve ; 3, lachrj'mal 

 branch ; 4, frontal ; 5, external 

 frontal or supraorbital ; 6, 

 internal frontal ; 7, supra- 

 trochlear branch ; 8, nasal 

 nerve ; 9, infratrochlear 

 branch ; 10, internal nasal 

 passing through the internal 

 orbital foramen ; 11, anterior 

 deep temporal pi'oceeding from 

 the buccal nerve ; 12, middle 

 deep temporal ; 13, posterior 

 deep temporal arising from the 

 masseteric ; 14, origin of the temporo-auricular ; 15, great superficial petrosal nerve. 



Course and distribution.— Cylindrical and firm, like the other 

 motor nerves, the third nerve, quitting the investment of the arachnoid 

 membrane, pierces the inner layer of the dura mater close to the poste- 

 rior clinoid process, and proceeds towards the sphenoidal fissure, lying 

 in the external fibrous boundaiy of the cavernous sinus. 

 _ The third nerve divides near the orbit into two parts, which are con- 

 tinued into that cavity between the heads of the external rectus muscle, 

 VOL. I. 31 jr 



