288 ALUS. [Vol. XVIII. 



its apparent origin. This nerve thus has an apparently double 

 origin, arising both from the fourth and third vagi. It undoubt- 

 edly receives a part, at least, of its fibers from the non-ganglionic 

 strand of the main vagus root. The branch is a long one. It 

 runs at first backward and slightly mesially to the hind edge of 

 the efferent artery of the fourth arch, which artery lies slightly 

 posterior to the hind edge of the transversus dorsalis posterior. 

 There it turns downward and forward behind and around the 

 artery, and runs forward ventral to the artery and then ventral 

 to the transversus dorsalis, lying between that latter muscle and 

 the anterior end of the retractor arcuum branchialium of its side 

 of the head. Running forward in this position, along the mesial 

 edge of the superior pharyngeal bone, it is distributed to tissues 

 there, certain of its branches perforating the third infrapharyngo- 

 branchial and going to general tissues on its ventral surface. One 

 branch of the nerve goes to the retractor muscle, and others to 

 the anterior extensions of the constrictor cesophagei. 



After giving off these two branches, and at some distance from 

 its ganglion, the fourth vagus separated, in one specimen, into 

 two nearly equal parts. In a second specimen it separated into 

 three parts, two of which first anastomosed, and then, separating, 

 one of the two strands united with the remaining third part of the 

 nervus, thus forming two principal nerves. These two parts of 

 the fourth vagus are the superior and inferior pharyngeal nerves 

 of the fish, both of which run backward, dorsal to the efferent 

 arteries of the third and fourth arches. The inferior nerve sends 

 branches to the interarcualis dorsalis that connects the fourth and 

 fifth arches, and then separates into two parts, both of which turn 

 downward and then forward over the posterior end of the gill 

 arches. One of these two parts reaches the grooved external sur- 

 face of the fourth ceratobranchial, at its proximal end, and be- 

 comes the ramus posterior of the fourth arch. It is accordingly 

 the ramus pretrematicus of the fourth vagus. From it, before 

 it reaches the grooved surface of the ceratobranchial, certain deli- 

 cate branches are given off, some of which go to the tissues of the 

 pharynx, and apparently represent pharyngeal elements of the 

 nervus, while others apparently innervate the adductor muscle of 

 the fifth arch. The other branch of the main nerve reaches the 



