368 MANUAL OF ELEMENTARY ZOOLOGY 



through its foramen into the orbit of its own side, where 

 it supplies the superior, inferior, and internal recti muscles 

 of the eye by short branches and gives a long branch across 

 the floor of the orbit to the inferior oblique. The slender 

 fourth, trochlear, or patheticus nerve arises from the dorsal 

 surface of the brain between the optic lobes and the 

 cerebellum, and passes out through a special foramen to 

 supply the superior oblique muscle of its side. The sixth 

 or abducent nerve is also slender. It arises from the 

 ventral side of the medulla and supplies the external rectus 

 muscle, passing through the same foramen as the main 

 ■branches of the fifth and seventh nerves. The latter two 

 nerves, with the eighth, arise close together from the sides 

 of the medulla below the restiform body. The fifth or 

 trigeminal has three branches. Of these the first, or 

 ophthalmic, parts at once from the rest of the nerve, turns 

 forward within the skull, passes through a foramen in the 

 side of the cranium above the recti muscles, and runs 

 forwards along the outer side of the cranial wall, together 

 with the similar branch of the seventh nerve, to leave the 

 orbit by a foramen above the nasal capsule and be distri- 

 buted to the skin of the snout. The rest of the nerve leaves 

 the cranium by a large foramen below the recti muscles 

 and runs outwards across the orbital floor as a broad band, 

 which divides into a maxillary branch to the upper jaw 

 and a mandibular branch to the lower. The seventh or 

 facial nerve has a complicated distribution : it possesses (i) 

 an ophthalmic branch which, leaving the cranium by a 

 foramen in front of the similar branch of the fifth, accom- 

 panies the latter ; (ii) a buccal branch, which joins the main 

 branch of the fifth within the skull, crosses the orbit with 

 it, leaves it before it divides, and is distributed to certain 

 sense organs (neuromast organs, p. 373) of the side of the 

 face ; (iii) a small palatine branch which runs across the 

 floor of the orbit behind the fifth nerve and supplies the 

 roof of the mouth ; and (iv) a large hyomandibular branch 

 which runs outwards in the hinder wall of the orbit and 

 passes down the hyoid arch. This branch gives off a small 

 prespiracular branch to the anterior wall of the spiracle, 

 after which it passes as the postspiracular nerve behind the 

 spiracle and divides into three branches — an internal and 



