Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 



213 



directly forward, passes ventral to the transversus dorsalis pos- 

 terior, and is inserted, ventral and mesial to that muscle, on the 

 mesial edge of the anterior end of the fourth infrapharyngo- 

 branchial and on the posterior end of the third infrapharyngo- 

 branchial. It is innervated by branches of a nerve that has its 

 apparent origin from the fourth vagus near the ganglion of that 

 nerve, or from that ganglion itself. When carefully traced prox- 

 imally, beyond its apparent origin, this nerve seems to receive a 

 large part of its fibers from the third or second vagus nerves, a 

 part of its fibers also coming from the commissural branch that 

 arisee from the main truncus of the united vagi and has been re- 

 ferred to in describing the innervation of the obliquus dorsalis of 

 the second arch. 



The Adductores Arcuum Branchialium are two in number, 

 one on the fourth arch and one on the fifth. The adductor of the 

 fourth arch is a small muscle lying in the angle between the epi- 

 branchial and ceratobranchial of its arch. It is apparently inner- 

 vated by branches of that branch of the anterior nerve of the arch 

 that passes over the antero-lateral edge of the arch onto and along 

 the oral surface of the ventral part of the arch ; that is, by a 

 branch of the ramus posttrematicus of the third vagus. 



The adductor of the fifth arch is a short, stout muscle which 

 arises from the dorso-lateral surface of the fifth ceratobranchial, 

 near its posterior, pointed end, and is inserted mainly on the inner 

 surface of the small piece of cartilage that represents either the 

 epibranchial or infrapharyngobranchial of the fifth arch. Some 

 of the fibers of the muscle extend forward beyond this element of 

 the fifth arch onto the adjoining articulating ends of the cerato- 

 branchial and epibranchial of the fourth arch. It is apparently 

 innervated by branches of that branch of the fourth vagus nerve 

 that innervates the fifth interarcualis dorsalis. 



The Interarcuales Yentrales are represented in Scomber by 

 rudimentary obliqui ventrales, by two pharyngo-claviculares and 

 a pharyngo-hyoideus on each side of the head, and by two trans- 

 versi ventrales. The ventral interarcual ligaments, found so well 

 developed in Aiiiia and there considered as the true interarcual 

 muscles of the fish, are not found in Scomber; or, if found, they 

 are represented by ligamentous tissues only W'hich extend from 

 arch to arch along the basal line. 



