EYE-MUSCLE NERVES IN NECTURUS 157 



dorsal to the optic foramen. Running now for a distance of 

 about 3 mm. in its bony canal, which inclines sharply cephalad, 

 the oculomotor nerve emerges from the parietal bone about 4.8 

 mm. caudad to the emergence of the optic nerve; a point about 

 at the level of the preoptic nucleus in the brain. Here the nerve 

 lies in the trabecular cartilage immediately ventral to the r. oph- 

 thalmicus profundus V, and passing cephalad and very slightly 

 laterad in the same relation, divides into its ventral and dorsal 

 rami about 0.7 mm. cephalad to the foramen of exit of the optic 

 nerve from the parietal bone; a point about at the level of the 

 entrance of the olfactory tract in the olfactory bulb. 



The dorsal ramus now passes dorsad to the optic nerve and 

 running medial to or piercing the r. ophthalmicus profundus V, 

 reaches the common origin of the recti muscles (figs. 5 and 7). 

 Here it applies itself closely to the superior rectus muscle and 

 breaks up on the dorso-medial surface of this muscle about its 

 middle (fig. 5). 



There are usually present one or two small twigs, containing 

 two or three fibers, which leave the dorsal ramus of the oculo- 

 motor nerve to enter the bulbar fascia (fig. 5). Occasionally 

 some of these fibers may be traced to the eyeball but most of 

 them are lost among the blood vessels of the bulbar fascia. 



The ventral ramus of the oculomotor nerve, running imme- 

 diately ventral to the r. ophthalmicus profundus V and ventro- 

 lateral to the optic nerve, reaches the common origin of the recti 

 muscles and passes directly out on the ventral face of the inferior 

 rectus muscle (fig. 6). Quite frequently the ventral ramus enters 

 the inferior rectus muscle and in several cases was seen to lie 

 entirely dorsal to this muscle (fig. 7). 



During its passage cephalo-laterad on the inferior rectus mus- 

 cle, several twigs rise from the ventral ramus of the oculomotor 

 nerve which enter this muscle and, having reached its ventro- 

 medial edge, the ventral ramus splits into two branches one of 

 which runs directly to the medial rectus muscle, and the other, 

 passing along the medial border of the inferior rectus finally 

 enters the inferior oblique muscle near to its insertion on the 

 eyeball (fig. 6). 



