CRANIAL NERVES. 137 



portio facialis (sof), the buccal (Bu), and the hyomandibular nerves 

 (Fa', ch, Hm'}. The two first of these and the external mandi- 

 bular branch of the last innervate the sense organs of the sensory 

 tubes. The hyomandibular * excluding the external mandi- 

 bular branch may be called the facial proper (ch) ; it is a mixed 

 nerve for the hyoid arch with branches to the roof of the mouth 

 (palatine) and mandibular arch (prespiracular). 



The three roots of the facial are as follows: a dorsal root (Fa), from 

 which probably most of the lateral-sense organ nerves are derived, and 

 two ventral roots, of which the anterior is just behind the root of the 

 oth and is possibly double, while the posterior is just in front of the root 

 of the auditory. 



The ophthalmicus superfecialis freely communicates with the 

 buccal nerve as it passes through the cranial wall which it does 

 by a foramen dorsal to that for the trigeminal. Outside the 

 cranium it presents a ganglion and passing along the dorsal side 

 of the orbit is distributed to the supraorbital branch of the ceph- 

 alic lateral line and to the ampullae of the ampullary canals of 

 the snout. 



The buccal nerve (bu, bu') after passing through the cranial 

 wall with the trigeminus becomes closely applied to the gas- 

 serian ganglion and swells into a ganglion. It runs along the 

 floor of the orbit close to the maxillary nerve. It supplies the 

 inner and outer buccal groups of ampullae, and the sense organs 

 of the orbital and suborbital lateral line. 



The hyomandibular nerve, after leaving the skull by a foramen 

 which is generally through the auditory cartilage, behind and 

 distinct from the trigeminal, dilates into a ganglion where it gives 

 off forward the palatine nerve (indicated but not marked in the 

 figure). The palatine nerve at once gives off the prespiracular 

 nerves which are supposed to be homologous with the chorda 

 tympani of mammals, and is continued to supply the roof of the 

 mouth. It is homologised with the great superficial petrosal 

 of mammals. The hyomandibular then gives off a branch to 

 the mandibular and hyoid group of ampullae and lateral line 

 the external mandibular and is continued to the muscles, etc., 

 of the hyoid arch (internal mandibular of Stannius, ch). 



The auditory nerve arises by a root immediately behind 



* In the figure the hyomandibul ar nerve (ch) is smaller than the external 

 mandibular which runs with it, so that it appears as a branch of the latter. 



