Nos. iAND_'.] ANATOMY OF SCOMBER SCOMBER. 207 



on the skull, but on the outer surface of the jugular vein as that 

 vein issues from the facial foramen. The pretrematic branch of 

 the glossopharyngeus and the external carotid artery run forward 

 between the two heads of the muscle. 



The externus of the third arch lies, at its origin, immediately 

 in front of the anterior edge of the posterior internus. It runs 

 downward and backward immediately external to that muscle, 

 lying approximately parallel to the second externus, and is inserted 

 by tendon near the posterior end of the suprapharyngeal process 

 of the third epibranchial. It is almost entirely tendinous through 

 approximately the middle third of its length, this tendinous part 

 lying directly external to the posterior internus. It lies, toward its 

 insertion, between the ramus posttrematicus of the second vagus 

 nerve and the ramus pretrematicus of the third vagus. It is 

 innervated b}' a small branch of the second vagus, that usually 

 arises from the trunk of the nerve before it separates into its pre- 

 and post-trematic portions. In one specimen this branch arose 

 from the pretrematic part of the nerve, close to its base. 



The externus of the fourth arch lies, at its origin, immediately 

 behind the two interni. It runs downward and backward, ap- 

 proximately parallel to the third externus, and is inserted by a 

 long tendinous end on the postero-mesial edge of the fourth epi- 

 branchial, immediately distal to the bend that separates the prox- 

 imal articular head of that bone from its shank. It lies, at its 

 insertion, between the anterior and posterior branches of the 

 third vagus. It is innervated by a small branch that arose in 

 one specimen from the trunk of the third vagus, close to the 

 ganglion of the nerve, and in another specimen from the trunk 

 of the second vagus close to its ganglion. The latter specimen 

 was the first one in which the nerve was traced, and the nerve 

 fibers were not followed beyond their apparent origin from the 

 second vagus. In the second dissection, where especial attention 

 was given to it, it was found arising, as stated above, from the 

 third vagus ; and that was undoubtedly its real origin in the earlier 

 dissection also. 



The so-called fifth externus is tendinous at its origin, and is 

 there practically continuous with the lower edge of that part of 

 the first intermuscular septum that arises from the hind edge of 



