THE N. OCULOMOTORIUS. 23I 



Leaving the brain along the lateral face of the lobi 

 inferiores, it passes at once through the cranial wall, 

 which is here membranous, under the ventral edge of the 

 sphenotic bone and mesially of the m. rectus externus. 

 The m. rectus superior and the m. rectus internus lie 

 farther ventrally. The III nerve contains at its exit from 

 the brain chiefly the typical very large motor fibres; never- 

 theless there are mingled with these many of medium or 

 small size, though all are heavily myelinated. The finer 

 fibres tend to gather on the lateral aspect of the trunk and 

 some of them go out with each of the rami. The larger 

 part, however, enters the radix breva of the ciliary 

 ganglion. 



Under the cephalic end of the Gasserian ganglion it 

 gives off first the branch for the m. obliquus inferior, then 

 divides into dorsal and ventral portions, the former for 

 the m. rectus superior the latter for the mm. recti internus 

 and inferior. 



The branch for the m. obliquus inferior pursues a 

 rather peculiar course. Turning sharply ventrad and a 

 little mesad and caudad, it runs down the cephalic face of 

 the m. rectus externus from its dorsal to its ventral side, 

 then curving around the outer side of the m. rectus supe- 

 rior from the dorsal to the ventral side of this muscle, it 

 turns inward across the caudal face of the m. rectus infe- 

 rior and around the ventral side of the m. rectus internus, 

 closely wedged in between the latter muscle and the 

 origin of the m. adductor arcus palatini. In this narrow 

 space it crosses dorsally the r. palatinus without anasto- 

 mosis. Having reached the parasphenoid, it turns dorsad 

 between this bone and the m. rectus internus and then 

 cephalad dorsally of the parasphenoid, mesially of the m. 

 rectus internus and close under the optic chiasm, the 



