Nos. IAND2.] JXATOMY OF SCOMBER SCOMBER. 287 



lateral edges of the epibranchials of their respective arches. These 

 two principal portions of the ramus posttrematicus of this arch 

 thus seem, when compared with the corresponding nerves on the 

 anterior arches, to have shifted backward and downward around 

 their arch, the anterior part of the nerve being, on this arch, the 

 main nerve of the arch, and the posterior portion being an oral 

 branch. The posterior portion innervates the adductor muscle 

 of the arch, and it is to be noted that on the anterior arches no 

 adductor muscle is found. The anterior part, which is, in 

 position, the ramus anterior, or principal nerve of the arch, in- 

 nervates no muscles whatever, so far as could be determined, 

 though delicate branches of it may perhaps go to the obliquus 

 ventralis of the fourth arch and to the transversus ventralis 

 anterior. 



From the main truncus of the nervus, close to its ganglion, a 

 delicate branch is sent to the external levator of the fourth arch. 

 In the first specimens examined this nerve had its apparent origin 

 from the truncus of the second vagus, and was considered by Dr. 

 Dewitz as a branch of that nerve. As this seemed unusual an- 

 other specimen was examined, with the same result, but it was 

 found on further examination, that this branch could be separated 

 from the second vagus and traced to the third vagus. In still 

 another specimen the branch arose from the third vagus alone. 



The Fourth Vagus Nerve gives off, from its root, proximal 

 to its ganglion, or from the ganglion itself, a delicate branch 

 which goes to that levator muscle that has its insertion on the 

 clavicle. From the distal end of the ganglion, or from the trunk 

 of the nerve beyond the ganglion, another branch has its apparent 

 origin. When the ganglion is carefully cleaned this branch is 

 seen to be formed by two strands, one of which arises from the 

 fourth vagus, while the other and larger one can be traced prox- 

 imally, along the inner surface of the fourth vagus and its gang- 

 lion, to the third vagus. Where it joins the third vagus that 

 nerve is also joined by one of the four branches of the bundle of 

 fibers that pass outward from the main root of the vagus without 

 entering the ganglionic formations. A second branch of this 

 same bundle joins the fourth vagus close to the point where the 

 first mentioned strand of the nerve here under consideration has 



