380 H. W. NORRIS AND SALLY P. HUGHES 



The second division of the hypobranchial nerve, derived from 

 the motor constituent of the first spinal nerve, runs anteriorly 

 somewhat dorsal to the first division. At first it passes along 

 the lateral border of the esophagus, just outside its muscular 

 wall, farther anteriorly ventral to the lateral part of the pharynx, 

 then at the mesial dorsal border of the fifth ceratobranchial 

 cartilage, and still farther anteriorly ventral to it. It then unites 

 with the first branch, as already described. At the union of the 

 two nerves apparently all of the sensory elements of the first 

 division have been given off in minute nerves to the ventral and 

 ventrolateral skin in the branchial and postbranchial region, and 

 from this point onward the hypobranchial nerve is exclusively 

 motor. Anterior to the shoulder girdle, the motor hypobran- 

 cbialis innervates the coraco-arcualis communis, coracomandibu- 

 laris, coracohyoideus, and coracobranchiales muscles. 



Neal ('97) derives the hypoglossal musculature of Squalus 

 from the fourth to the eighth postotic somites. The second and 

 third postotic somites are present; the second is rudimentary, 

 and the third is without a ventrally growing bud, but with a 

 nerve. From the fourth somite comes the coracomandibularis 

 muscle, apparently. The fifth to the eighth somites produce 

 muscles between the hyoid and procoracoid cartilages. The 

 seventh and eighth somites also contribute to the pectoral plate. 

 If one takes into account the occurrence of as many as five pairs 

 of occipital nerves in the pup stage, it is seen that there is slight 

 discrepancy between the account given by the writers and that 

 of Neal relating to an earlier stage. 



According to van Wijhe, the hypoglossus nerve is derived from 

 three (apparently four) ventral roots of the seventh, eighth, and 

 ninth somites, on the last of which is a sympathetic ganglion. 

 In Squalus the writers find a small sympathetic ganglion on the 

 ventral root of the third spinal nerve. 



Individual variation in the derivatives of the somites and their 

 corresponding nerves probably explains the minor discrepancies 

 between the accounts of various writers. 



Comparing the hypobranchial nerve of selachians with the 

 hypoglossal nerve of amphibians, we see some suggestive re- 



