16 



V. The trigeminal arising in conjunction with the 7th and 8th nerves from the 



medulla and dividing into three branches : — 



(a) The first branch, — orbito-nasal, — consisting of a dorsal division which 



passes forwards over the muscles of the eye, and a ventral which 

 passes over the external rectus, but under the superior and internal 

 recti and superior oblique, to meet and unite with the dorsal branch — 

 the common trunk then passes to the nasal capsule, within which it 

 divides into two branches, one running transversely over the nasal 

 sac, while the other passes forwards to the rostrum to supply the 

 gelatinous tissue, etc., in the anterior region of the head. 



(b) The second branch runs forwards external to the orbito-nasal and 



divides into two branches — (1) the palato-nasal which passes beneath 

 the muscles of the eye to supply the ventral parts of the rostrum, 

 fronto-nasal process, etc. ; and (2) the maxillary which supplies the 

 upper jaw, antorbital cartilage, etc. 



(c) The third branch — mandibular — which runs forwards parallel to the 



maxillary nerve, and supplies the mandible and part of the upper jaw. 



VI. The abducens leaving the skull, close to the 5th and 7th nerves, to 

 supply the external rectus muscle of the eye. 



VII. The facial, which, after passing through its foramen in the skull, divides 

 into two branches — (a) the palatine nerve, which passes in front of the 

 spiracle to supply the pseudo-branchise and mucous membrane of mouth ; 

 (6) the hyomandibular, which passes outwards in front of the auditory 

 capsule to be distributed over the hyomandibular cartilage, jaw muscles, 

 etc., and supply small branches (chorda tympani) to the mandible. 



VIII. The auditory entering the anterior part of auditory capsule to send 

 branches to the vestibule and ampullae. 



IX. The glossopharyngeal passing obliquely through the ventral portion of 

 auditory capsule to be distributed round the first gill cleft (hyoid half-gill 

 and anterior half-gill of first branchial arch.) 



X. The vagus passing backwards close to the auditory capsule and along the 



anterior vertebral plate to send four branches to the gills of the four posterior 

 gill clefts, and then dividing into a ventral (gastric and cardiac) branch, 

 and a lateral branch which supplies the sensory tubes, etc. 

 Make a sketch showing the distribution of the cranial nerves. 

 Examine the spinal nerves ; observe that each arises by two roots which pass 

 separately through the wall of the spinal column to unite outside ; note 

 that the first 16 nerves of eacb side unite to form the brachial plexus which 

 gives off branches to the pectoral fin, while the remainder supply the various 

 parts of the body walls, fins, etc. 



