44 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
fibers surround the vessel in a circular manner. For the remainder 
of the distance the fibers are diagonal or longitudinal to the wall of the 
vessel. Here the latter lies in immediate contact with the thymus 
gland. 
The muscle is innervated by some very fine rami (not included in 
plotting) from X and IX + X (Fig. K, rm. on. j.), as was determined 
by study of the sections. Some undetermined rami appearing in the 
dissection (Plate 3, fig. 7) are probably of like function. 
J. OCULOMOTOR NERVE. 
The oculomotor nerve (J//) arises from its nucleus of origin in the 
floor of the aqueduct of Sylvius and emerges as one large root from the 
ventral side of the mesencephalon (Plate 2, fig. 4). It swings laterad 
and cephalad to pass out of the cranium through the membranous 
wall, being covered laterally at this point by the bursalis muscle. 
(Plate 6, fig. 16). Posterior to the origin of the recti muscles the nerve 
divides into three large rami; the dorsal one goes to the dorsal rectus; 
a large ventral one, which later divides (Plate 5, fig. 14, JJ), supplies 
the ventral rectus, the anterior rectus and the ventral oblique; be- 
tween these two large rami is the short root of the ciliary nerve. The 
latter is composed chiefly of fine neuraxons, which may be recognized 
as a distinct bundle in the center of the main trunk from the point 
where it emerges from the brain to its separation from the somatic 
motor components as the ciliary root. Within the brain itself it could 
not be independently traced in this series. 
The branch of nerve III to the dorsal rectus muscle (Plate 2, fig. 4, 
rt. d.) isa large one. It follows the lateral face of this muscle near its 
anterior ventral edge (Plate 5, fig. 14), several successive bundles of 
fibers being given off to accomplish the innervation of the muscle. 
The large ventral ramus (Plate 5, fig. 15, II) passes mesad of the 
retractor oculi to attain a position on the ventral face of the ventral 
rectus muscle. It is in this part of its course that a group of long rami 
separate from it, and penetrate the ventral rectus from both the dorsal 
and ventral surfaces (Plate 2, fig. 4). The remainder of the nerve 
(Plate 5, fig. 14, III) passes cephalad close to the median line, dividing 
to send more than half of its fibers dorsally into the anterior rectus 
(Plate 5, fig. 13, rt. a.), the remainder passing on to the ventral oblique 
(Fig. 13, ob. 2.). 
* mi. s 
