370 hlERyOUS 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 

 meduUare anterius, as already described (Fig. 141, «). 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, /) 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, F) 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, k), from which three branches diverge. 

 One branch is joined by the ventral root (4), which passes over 

 tlie 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. 



I. 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 tiien laterad of the 



