37° NERVOUS SYSTEM. 
short ciliary nerves which pass along each side of the optic 
nerve to the eyeball. These nerves penetrate the sclerotic at 
the sides of the eyeball to be distributed to the ball. 
IV. N. TROCHLEARIS.—The fourth nerve, the trochlearis 
(or patheticus), arises from the lateral border of the velum 
medullare anterius, as already. described (Fig. 141, 2). It 
passes craniad, emerges through the orbital fissure in company 
with the oculomotor, abducens, and ophthalmic, passes dorsad 
of the superior rectus muscle, and reaches (Fig. 154, 7) the 
caudal border of the belly of the superior oblique muscle near 
its middle. It supplies only the superior oblique. 
V. N. TRIGEMINUS.—The fifth nerve, the trigeminus (or 
trifacial) arises (Fig. 138, V) by two roots, a large sensory and 
a small motor root (4), as already described (p. 347). One 
of these, the motor (4), is smaller and more ventral; the other, 
the sensory root, is larger and dorsal. The dorsal root soon 
enlarges to form a large ganglion, the semilunar (or Gasserian) 
ganglion (Fig. 138, 4), from which three branches diverge. 
One branch is joined by the ventral root (4), which passes over 
the ventral surface of the semilunar ganglion; and the nerve 
thus formed is the mandibular division (1) of the fifth nerve. 
Of the other two branches from the ganglion, the middle and 
longest is the maxillary nerve (2), and the smallest is the 
ophthalmic (3). The mandibular nerve is thus mixed, motor 
and sensory, while the others are sensory. 
1. N. ophthalmicus.—The ophthalmic or first division of 
the fifth nerve arises from the semilunar (or Gasserian) gan- 
glion. It passes out of the cranial cavity and into the orbit 
by way of the orbital fissure, in company with the third, fourth, 
and sixth nerves and with the extension of the carotid 
(arterial) plexus. 
It passes between the superior and medial recti along with 
the third nerve, crosses dorsad of the optic nerve, and divides 
into infratrochlear and ethmoidal branches. In the orbital 
fissure it gives off the frontal nerve, and while crossing the 
optic it gives off the long ciliary nerve. 
a. N. frontalis.—The frontal nerve passes along the lateral 
border of the superior oblique muscle and then laterad of the 
