158 PAUL S. McKIBBEN 



When the ventral ramus of the oculomotor nerve reaches the 

 common origin of the recti muscles there usually arise from it 

 one or two small twigs of two to four fibers, which, passing into 

 the bulbar fascia, finally reach the eyeball. Very often one of 

 these branches applies itself to the sheath of the optic nerve and 

 thus gains the eyeball (fig. 7). In several cases these twigs have 

 been seen to enter either the inferior oblique or the medial rectus 

 muscle; but usually one at least is present which reaches the 

 eyeball and this very often in company with the sheath of the 

 optic nerve. 



In three of the eyes examined there was present a small twig 

 from the ventral ramus of the oculomotor nerve which entered 

 the lateral rectus muscle along with the abducent nerve. 



A^. trochlearis 



The trochlear nerve rises from the caudal border of the dorsal 

 surface of the mid-brain and passes ventro-laterad and slightly 

 cepbalad, lying in the angle between the mid-brain and the ros- 

 tral border of the medulla oblongata and cerebellar commissure 

 (figs. 1, 3 and 8). The root of the nerve rises after decussation 

 immediately cephalad to the cerebellar commissure and contains 

 usually sixteen to twentj^-four fibers. A few fibers have been 

 observed which seem to enter the nerve uncrossed. These rise 

 from the caudal border of the optic tectum about 0.1 mm. from 

 the midline and at once seem to enter the main trunk of the 

 nerve. Four to eight such fibers usually appear on either side 

 in preparations stained with methylene blue. On careful exam- 

 ination under high magnification, these fibers seem to be larger 

 fibers than those which make up the trochlear nerve and to belong 

 to the mesencephalic root of the trigeminal nerve which lies here 

 beneath the trochlear nerve. Two or three smaller fibers from 

 the tectum have been observed which appear to enter the 

 trochlear nerve uncrossed. 



The work of Tczer and Sherrington ('10) shows that in mam- 

 mals the eye-muscle nerves contain sensory fibers (propriocep- 

 tive). If a similar arrangement exists in Necturus and the mes- 

 encephalic root of the trigeminal nerve is a sensory root, we may 



