CRANIAL NERVES OF CHIM^ERA MONSTROSA. 669 



the post-branchial, and has a precisely analogous course. It dips down and passes under 

 the second pharyngo-branchial, and divides into the same two branches. The transverse 

 branch, of course, innervates the levator muscle of the second arch, and not of the first. 



(8) Accessory visceral branch (a) (X 2 9 ). — Slips down through a notch on the outer 

 edge of the first pharyngo-branchial, and courses obliquely forwards and inwards direct 

 on to the pharynx. 



(9) Accessory visceral branch (b) (X 2 10 ). — Springs from the prse-branehial, and runs 

 obliquely downwards and forwards on to the pharynx. It passes under the second 

 branchial arch, and, after dividing into two, ends laterally on the pharynx, somewhat in 

 front of the second branchial arch. 



(10) Accessory visceral branch (c) (X 2 11 ). — This is a very fine nerve, and passes 

 downwards and forwards straight on to the pharynx. It arises from the prse-branchial. 



Vagus 3. 



Arises immediatelv behind and in contact with the root of vagus 2. It leaves the 

 vagus foramen in company with the latter, and lies underneath and slightly behind it. 

 The ganglion is obscured by that of vagus 2, but shortly afterwards the nerve takes a 

 backward turn and leaves vagus 2, passing over the first and second pharyngo-branchials. 

 Before it breaks up, it gives off a motor twig (X 3 4 ), and finally passing down a 

 similar groove in the common pharyngo-branchial (P B 1 ) to those described on the first 

 and second visceral arches, divides into the following nerves : — 



(1) Prse-branchial (X 3 1 ). — Distributed to seventh demi-branch. It runs at the base 

 of the gill to the base of the arch. No conspicuous branches were found, neither was the 

 nerve traced on to the pharynx. 



(2) Post-branchial (X 3 2 ). — Supplies eighth or last demi-branch. Dorsally and 

 laterally this nerve is in connection with its demi-branch and courses at its base, but 

 ventrally it approaches the arch, and on arriving at its base turns inwards, and passing 

 across the arch is continued on to the pharynx, where it divides into two or three 

 branches. There were no other obvious branches. 



(3) Accessory skeletal branch (X 3 s ). — Passes along the posterior edge of the fourth 

 branchial arch, but was not traced right round. It is a very slender nerve, and does not 

 give off any noticeable branches. 



(4) Motor branch (X 3 4 ). — The origin of this nerve from the main trunk of vagus 3 

 has been already described. It is a precisely similar nerve to (X 2 7 ) from the preced- 

 ing component of the vagus, and is distributed to the same muscle. 



(5) Visceral proper (X 3 5 ). — Dips down and passes under the common pharyngo- 

 branchial (P B 1 ). It then courses obliquely inwards and forwards, and reaches the 

 pharynx. There it divides into two main branches, which form a plexus. The inner 

 or posterior main branch pursues a transverse direction almost on to the mid-dorsal line. 

 This nerve (X 3 5 ) is one of the largest of the visceral branches. 



