x CEREBRAL NERVES 463 



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 main 

 parts 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] 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 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 (Mil p], 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 ky] which 

 passes behind the spiracle (first giving off small prespiracular branches 

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



