x CEREBRAL NERVES 463 



above the optic nerve. The pathetic (IV), coming off from 

 the dorsal side of the front end of the medulla oblongata 

 and supplying the superior oblique muscle, pierces the 

 cranial wall almost directly above the optic foramen (compare 

 also Fig. 126). All the other nerves arise from the ventro- 

 lateral regions of the medulla oblongata, the abducent, 

 supplying the external rectus muscle, coming off nearer 

 the middle line than, and anterior to, the others. The 

 abducent (VI) and the greater part of the trigeminal (V) and 

 facial (VII) nerves pass out through a single foramen in the 

 skull in the posterior and ventral part ^of the orbit, just 

 anterior to the auditory capsule. A short distance above 

 this foramen are two others, the ventral slightly anterior to 

 the dorsal : these transmit the ophthalmic branches (see 

 below) of the trigeminal and facial (V op, VII op] respec- 

 tively, and from them grooves pass along the dorsal side 

 of the orbit to an aperture just behind the olfactory capsule, 

 the nerves emerging again on the dorsal side of the skull. 

 The auditory nerve passes through a large foramen on the 

 inner side of the auditory capsule to supply the membranous 

 labyrinth. The glossopharyngeal (IX) emerges behind the 

 auditory capsule at the posterior end of a horizontal groove 

 in this region, and the vagus (X) passes out through a foramen 

 between the glossopharyngeal and the foramen magnum. 



The nerves supplying the integumentary sense organs are 

 as follows : (i) The ophthalmic branch of the facial (VII op) 

 runs, as we have seen, dorsally to the similarly named 

 branch of the trigeminal, close under the skin, and supplies 

 the sensory tubes and ampullae (see p. 464) of the upper part 

 of the snout ; those of the lower part of the snout are 

 innervated by (2) a buccal branch (VII b), which extends 

 along the floor of the orbit just above the maxillo-mandibular 

 division of the trigeminal ; and those in the region of the 

 hyomandibular by a small (3) external mandibular branch 

 (VII e. m), arising from the large hyomandibular nerve (see 

 below). The lateral-line canal, extending along the body 

 and tail, is supplied by (4) the lateral branch of the vagus (X /) 

 which runs backwards to the inner side of the rest of the 

 nerve and dorsally to the spinal nerves, along the inner side 

 of the body-wall, giving off branches which extend outwards 

 between the great lateral muscles to the lateral canal. 



The other branches of the facial are : a small palatine 

 (VII p), which extends along the floor of the orbit, just 

 behind the trigeminal, and supplies the roof of the mouth ; 

 and a large hyomandibular (VII hy) which passes behind the 

 spiracle first giving off small prespiracular branches 





