284 ALUS. [Vol. XVIII. 



anastomosed, so far as could be determined, with branches of the 

 posterior nerve of the arch. On the posterior arches also the 

 branches of the anterior and posterior nerves of the arch did not 

 anastomose. Scomber thus differing markedly in this respect from 

 Aviia. 



The Second Vagus Nerve separates, slightly beyond its 

 ganglion, into its anterior and posterior portions, both of which 

 run downward and slightly backward through a small triangular 

 space that lies between the hind edge of the posterior division of 

 the internal levator of the arches, the dorsal surface or anterior 

 edge of the obliquus dorsalis of the third arch, and the antero- 

 ventral edge of the external levator of the same arch. The anterior 

 portion of the nervus here separates into its pharyngeal and pre- 

 trematic parts. 



The pharyngeal branch of the nervus, running downward, 

 reaches the lateral surface of the posterior division of the internal 

 levator, where it lies between that muscle and the proximal edge 

 of the supraphar3aigeal process of the second epibranchial. Con- 

 tinuing downward it enters the tissues that lie on the dorsal sur- 

 face of the third infrapharyngobranchial, lateral to the insertion 

 of the levator muscle, and breaks up into several branches, some 

 of which penetrate the bone itself. 



The pretrematic branch of the nervus runs downward and lat- 

 erally till it reaches the dorsal surface of the suprapharyngeal 

 process of the second epibranchial, where it turns forward and 

 laterally on that process, and at its base reaches the dorsal sur- 

 face of the epibranchial. There it turns distally and continues 

 distally to the distal end of the arch, not differing in any im- 

 portant respect from the corresponding branch of the first vagus. 

 Both this branch and the posttrematic branch pass ventral to the 

 anterior continuation of the efferent artery of the third arch. 



The posttrematic branch of the nervus runs backward, down- 

 ward and laterally, crosses the dorsal surface of the interarcualis 

 dorsalis that connects the second and third arches, and reaches 

 the dorsal surface of the epibranchial of the third arch. There 

 it has a course and distribution not differing from that of the 

 corresponding branches on the two anterior arches. At its distal 

 end it separates into two branches, one of which passes internal 



