232 



THE CRANIAL NERVES. 



Sylvius opposite the upper part of the inferior quadrigeminal body (fig. 146). 

 From the nucleus the fibres are directed at first downwards for a short distance, and 

 then backwards and inwards, arching round the lower part of the aqueduct, to enter 



Fig. 151. PLAN OP THE ORIGINS OF THE THIRD AND 



FOURTH NERVES. (G. D. T.) 



The midbrain is supposed to be divided at different 

 levels on the two sides, the section on the right side of 

 the figure passing through the superior, and on the 

 left side through the inferior quadrigeminal body : III, 

 third nerve ; N.I II, its nucleus ; IV, fourth nerve ; 

 N.IV, its nucleus ; V.D, descending or mesenceohalic 

 root of the fifth nerve; N. V, its nucleus; C.Q.S, 

 superior, and C.Q.I, inferior quadrigeminal body; 

 P.L.B., posterior longitudinal bundle. 



the superior medullary velum, where they 

 cross to the opposite side, the two nerves 

 thus forming a complete decussation. 



Emerging from the upper end of the 



superior medullary velum close to the frenulum, and immediately below the 

 inferior quadrigeminal body, the fourth nerve is directed at first outwards 

 across the superior peduncle of the cerebellum, and then turns forwards 

 round the outer side of the crus cerebri (figs. 141, 147), lying parallel to 

 and between the posterior cerebral and superior cerebellar arteries. It enters an 



Fig. 152. VIEW FROM ABOVE OP THE UPPER- 

 MOST NERVKS OF THE ORBIT, THE GASSERIAN 



GANGLION, &c. (From Sappey, after Hirsch- 

 feldandLeveille".) 



I, olfactory tract, passing forwards into the 

 bulb; II, optic commissure; III, oculomotor; IV, 

 trochlear nerve ; V, large root of the fifth nerve, 

 a small portion of the lesser root is seen below 

 it; VI, sixth nerve ; VII, facial ; VIII, audi- 

 tory ; IX, glosso-pharyngeal ; X, pneumo-gastric ; 

 XI, spinal accessory ; XII, hypoglossal : 1, Gras- 

 serian ganglio^ ; 2, ophthalmic nerve ; 3, lachry- 

 mal nerve ; 4, frontal ; 5, external, 6, internal 

 branch of the supraorbital nerve ; 7, supratro 

 chlear nerve ; 8, nasal nerve ; 9, its infratro- 

 chlear branch ; 10, nasal nerve, passing through 

 the anterior internal orbital canal ; 11, anterior 

 deep temporal proceeding from the buccal nerve; 

 12, middle deep temporal ; 13, posterior deep 

 temporal arising from the masseteric ; 14, origin 

 of the auriculo-temporal ; 15, great superficial 

 petrosal nerve. 



aperture in the dura mater immediately 

 beneath the free margin of the ten- 

 torium, a little behind the posterior 

 clinoid process, and runs forwards in 

 the outer wall of the cavernous sinus, 



resting against the upper margin of the ophthalmic nerve, and crossing the third 

 obliquely on its outer side from below upwards, to the inner end of the sphenoidal 

 fissure. Passing into the orbit above the external rectus muscle, it inclines inwards 

 over the levator palpebrae and superior rectus, and finally enters the superior oblique 

 muscle on its upper surface, and close to its outer border. 



