Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 283 



nerve separates from the pharyngeal and pretrematic parts of the 

 nervus, and innervates the external levator of the second arch. 

 The next branch, in the specimen used for illustration, was a 

 delicate one which fused wdth four delicate branches of the ramus 

 pretrematicus to form the plexus, already described, that in part 

 innervates the interarcualis dorsalis of the first and second arches. 

 The next branch is a large one, and is given ofif as the main nerve 

 approaches the distal end of the epibranchial of the arch. It 

 is sometimes single and sometimes double at its origin, the two 

 parts in the latter case soon uniting again to form a single nerve. 

 It turns laterally and then downward over the antero-lateral edge 

 of the epibranchial, and passing internal to the degenerate inter- 

 branchial muscle of the arch reaches the dorsal or oral edge of 

 the antero-lateral surface of the ceratobranchial. As it passes 

 the ventral or oral edge of the antero-lateral surface of the epi- 

 branchial, a large branch is sent proximally along that edge ; and 

 as it traverses the angle between the epibranchial and cerato- 

 branchial a number of delicate branches are sent to the degenerate 

 interbranchial muscle of the arch. The main branch then con- 

 tinues distally to the distal end of the arch, lying at first near the 

 dorsal or oral edge of the antero-lateral surface of the cerato- 

 branchial of the arch, and, beyond that element, near the corre- 

 sponding edge of the hypobranchial. It gives off, in this part of its 

 course, many delicate branches, thus resembling in every respect 

 the corresponding branch of the corresponding nerve of the first 

 arch. 



The main ramus posttrematicus, after giving oft* this large 

 anterior or oral branch, reaches the ventral aspect of the cerato- 

 branchial, and at the distal end of that element passes onto the 

 ventral surface of the degenerate obliquus ventralis of the arch. 

 Toward the anterior end of that muscle, it perforates the hypo- 

 branchial of the arch and appears on its antero-lateral surface, 

 where it turns upward and breaks up into delicate terminal 

 branches which run forward and backward along the antero- 

 lateral surface of the hypobranchial and the adjoining lateral 

 surface of the basal elements. While on the ventral aspect of 

 its arch one or more branches are given off by the nerve, but, 

 as on the first arch, no branch in the full length of the nerve 



