CRANIAL NERVES OF CHIMERA MONSTROSA. 667 



Vagus 1. 



Arises immediately posterior to the large root of tlie glosso-pliaryngeal. On emerging 

 from the vagus foramen it courses slightly forwards, and expands into its ganglion at 

 about the same level as the glosso-pharyngeal. It then runs parallel to the latter for 

 some little distance, but afterwards takes a posterior turn, and passing down a groove 

 bored in the outer face of the first pharyngo-branchial, divides into the fullowing 

 branches (I did not succeed in finding a dorsal branch to vagus 1) : — 



(1) Prse-branchial (X l 1 ). — Distributed partly to the third demi-branch. This 

 nerve is undoubtedly homologous to a prse-branchial nerve, although it is distributed 

 rather to the pharynx at the base of the third demi-branch. Dorsally it is in connection 

 with the demi-branch, but ventrally, and especially the small branch X l 2 and the long 

 anterior branch X l 3 (from which a slender pharyngeal branch X l 4 was given off, which 

 was not traced), it undoubtedly innervates the pharynx at the base of the gill. 



(2) Post-branchial (X l 5 ). — Innervates the fourth demi-branch. This nerve some- 

 what resembles the pree- branchial. It is undoubtedly in connection with its demi-branch 

 dorsally, but ventrally it innervates the pharynx at the base of the gill. Finally, it is 

 continued for a short distance beyond the arch straight on to the pharynx, where it 

 divides into a few branches. This is the largest division of Vagus I, but has no 

 conspicuous branches. 



(3) Extra-branchial nerve (X 1 G ). — This arises, as shown in fig. 2, in a somewhat 

 complicated way from the accessory skeletal branch X l 8 . It is a very fine nerve, and 

 is distributed to the fourth demi-branch. 



(4) Accessory skeletal branch (a) (X l 7 ). — Courses along the anterior edge of the 

 second branchial arch. I succeeded in tracing it almost to the base of the arch, but did 

 not find that it had any obvious branches. 



(5) Accessory skeletal branch (b) (X l 8 ). — Euns close to the posterior edge of the 

 second branchial arch. It is perceptibly smaller than X l 7 , and was traced to the base 

 of the arch. There were no conspicuous branches. 



(6) Motor-branch (X l 9 ). — This nerve is precisely comparable to the motor branch 

 of the IXth. It arises, however, from the prse-branchial. After running forwards for a 

 short distance it divides into two branches (X l 10 , X l 11 ), both of which pass under the 

 hyoid arch and are distributed to the same muscle supplied by the anterior division of 

 the motor branch of the glosso-pharyngeal (IX 9) accompanying and lying ventral to 

 this latter nerve. 



(7) Visceral proper (X l 13 ). — This dips down and passes inwards and backwards 

 under the pharyngo-branchial of the first branchial arch. Whilst under the arch it 

 divides into two branches, of which one (X l 14 ) continues in the transverse direction, and 

 supplies the levator muscle of the first branchial arch. The other branch (X l 15 ) takes 

 a forward turn, and is distributed to the pharynx in the vicinity of the same arch. 



(8) Accessory visceral branch (X l 12 ). — The accessory visceral in the natural position 



