NERVES OF THE DOGFISH 381 



semblances. The hypoglossal nerve of the urodele amphibians 

 is formed from the ventral branches of one or more spinal nerves. 

 In some forms, as Siren, sensory elements are contributed at the 

 origin of the nerve, to be given off before the true hypoglossal 

 nerve is reached. In the caecilians sensory elements are like- 

 wise found at the origin of the nerve, and in some species of cae- 

 cilians an occipital nerve forms part of the hypoglossal. The 

 ventral musculature supplied by the hypobranchial nerve in 

 selachians undoubtedly corresponds in a general way to the ven- 

 tral musculature anterior to the shoulder-girdle in amphibians. 

 In Siren, for example, where the hypoglossus is derived from two 

 or three spinal nerves, it innervates not only the geniohyoid 

 muscle, but also in part the sternohyoideus, abdominohyoideus, 

 and other trunk muscles. In the caecilians, in which it is de- 

 rived from the first and second spinal and sometimes from the 

 occipital as well, it innervates not only the geniohyoideus and 

 hyoglossus, but also parts of the thoracicohyoideus and ab- 

 dominohyoideus and other trunk muscles. 



In general the hypobranchial nerve and musculature of se- 

 lachians corresponds to the hypoglossal nerve and musculature 

 of amphibians. There would seem little difficulty in deriving 

 the amphibian hypoglossal from the selachian hypobranchial. 



SYMPATHETIC GANGLIA CONNECTED WITH CRANIAL NERVES 



The writers frankly disclaim any attempt at a description of 

 the sympathetic nervous system in Squalus. Rather, there fol- 

 low notes on the occurrence of certain ganglia, observed some- 

 what incidentally during the preparation of the main body of 

 this research. Some of these ganglia have been seen and men- 

 tioned by previous writers, but as far as the writers know there 

 has been no comprehensive treatment of the subject, as far as 

 it concerns the selachians. These fragmentary observations are 

 about all that could be made upon the material available. A 

 special research upon material prepared especially for the invest- 

 igation of sympathetic nervous tissue in the elasmobranch fishes 

 should yield valuable results. The results of somewhat desultory 



