NERVES OF THE DOGFISH 367 



results from the plexus, extending posteriorly nearly to the first 

 dorsal fin. 



Fibers of the ramus dorsalis are distributed through a vari- 

 able number of nerve ramuli to the section of the main sensory 

 canal immediately posterior to that innervated by the ramus su- 

 pratemporalis X. In one specimen there are eight of these ramuli; 

 in a second specimen eleven. It should be noted, however, that 

 in the first one the ramus supratemporalis X has six ramuli, 

 and in the second four. That is, there seems to be a sort of re- 

 ciprocal arrangement of ramuli between the rami supratemporalis 

 and dorsalis. Besides innervating the sensory canal, the ramus 

 dorsalis supplies a dorsal series of pit organs extending from im- 

 mediately posterior to the commissural canal nearly to the first 

 dorsal fin. In the specimen from which figure 50 was made there 

 are twenty-five of these pit-organs on the left side. It is a debat- 

 able question whether the ramus dorsalis as here defined is a 

 single nerve, but the presence of anastomoses between its divi- 

 sions precludes any exact separation between them. In Mus- 

 telus the ramus dorsalis is formed in a similar fashion from two 

 or three small nerves. 



5. General cutaneous elements in the vagus nerve of elasmobranchs 



It has been quite generally assumed that the vagus nerve of 

 selachians contains somatic sensory elements. The rami supra- 

 temporalis and dorsalis have been commonly designated as dor- 

 sal cutaneous branches of the vagus. The writers confess to 

 being seriously misled by this general assumption in the early 

 part of this research. 



Stannius finds a single dorsal branch of the vagus in selach- 

 ians, which he regards as lateral-line exclusively. Ewart and 

 Cole believe that the supratemporal branches of both the glosso- 

 pharyngeus and the vagus of Laemargus contain cutaneous as 

 well as lateralis elements. Cole finds in Chimaera a dorsal 

 branch of the ninth nerve supplying the skin, but not special 

 sense-organs. A dorsal branch of the vagus, on the other hand, 

 innervates canal organs. Kappers ('14) finds cutaneous con- 



