286 ALUS. [Vol. XVIII. 



The Third V^agus Nerve runs backward and downward, 

 ventro-mesial to the external levator muscles of the third and 

 fourth arches, and approximately parallel to them. At some 

 distance from its ganglion it separates into its anterior and pos- 

 terior portions. The former is a slender nerve which, turning 

 slightly laterally, runs downward, backward and laterally, between 

 the external levators of the third and fourth arches, and passing 

 dorsal to the obliquus dorsalis of the third arch reaches the dorsal 

 surface of the suprapharyngeal process of the third epibranchial. 

 There it separates into its pharyngeal and pretrematic branches. 

 The former continues backward and downward, and traverses the 

 space between the postero-mesial edge of the suprapharyngeal proc- 

 ess of the third epibranchial and the adjacent antero-lateral edge 

 of the fourth epibranchial, lying immediately lateral to the surface 

 by which the two elements articulate, and immediately mesial to 

 the mesial edge of the interarcualis dorsalis that connects the 

 two arches. It sends a branch to the interarcual muscle, apparently 

 innervating it, and turning mesially and downward enters the 

 tissues on the dorsal surface of the fourth infrapharyngobranchial. 

 The pretrematic branch of the nervus reaches the dorsal surface 

 of the third epibranchial and has a course and distribution similar 

 to that of the corresponding nerves on the anterior arches. 



The posttrematic branch of the nervus runs downward, back- 

 ward and laterally, between the external levator of the fourth 

 arch and that levator that has its insertion on the clavicle, and 

 reaches the dorsal surface of the fourth epibranchial, where it 

 separates into two parts. The larger of these two parts continues 

 distally along the dorsal surface of the epibranchial, passing ven- 

 tral to the anterior prolongation of the efferent artery of the arch, 

 and reaches the antero-lateral aspect of the main artery; where 

 it continues distally as the ramus anterior of the arch. The 

 other part turns downward and backward, ventral to the main 

 efferent artery of the arch, immediately dor so-mesial to the point 

 where that artery gives off its anterior prolongation. Crossing 

 the postero-mesial edge and surface of the fourth epibranchial 

 it reaches the oral surface of the fourth ceratobranchial, where 

 it has a course and distribution similar to that of the branches 

 which, on the anterior arches, run downward over the antero- 



