IX CEREBRAL NERVES 447 



cranial wall almost directly above the optic foramen (compare also Fig. 

 117). 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 main parts of the trigeminal (V) xcA facial i^W) 

 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) respectively, 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 ■- large 

 foramen on the inner side of the auditory capsule to supply the mem- 

 branous 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 sensory organs are as 

 follows: (l) The ophthalmic branch of the facial {Vll 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. 448) 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 I), 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 : — asmall/a/a/2'««(VII/), which 

 extends along the floor of the orbit, just behind the trigeminal, and sup- 

 plies the roof of the mouth ; and a large hyomandibular (VII hy) which 

 passes behind the spiracle — first giving off scaaW prespiracular branches 

 (VII p. s) to its anterior wall, extends along the anterior border of the 

 auditory capsule arid the posterior wall of the orbit, just beneath the 



