92 



THE ELASMOBRANCH FISHES 



In Heptanch us maculatus a first ventral constrictor is closely united with 

 the second, which as an immense sheath passes from the midventral line to be 

 inserted on the mandibular and hyoid arches. By removing a V-shaped seg- 

 ment from the anterior third of the mandible and hyoid, it will be seen that 

 this bundle is separated into superficial fibers to the 

 mandible and deeper fibers to the hyoid cartilage. 



The third to the eighth ventral constrictors arise simi- 

 larly from the midventral, triangular seam. Their su- 

 perficial fibers are continuous with those of the third to 

 the eighth dorsal constrictors (fig. 92). The deeper slips 

 or interbranchial parts of these muscles pass through 

 the eoracobranchial muscles and are inserted on the 

 neck of the ceratobranchial cartilages {ihv., fig. 95). 



The trapezius muscle {tr., fig. 92) arises from the side 

 of the dorsal longitudinal liundle and passes backward 

 and downward between this bundle and the dorsal con- 

 strictors. A ^^11 slip of it is attached to the upper part 

 of the last arch, but most of its fibers are inserted on the 

 scapula which it draws forward. 



INTERARCUALES 



The interarcuales (fig. 94) are deep muscles which bind 

 the branchial arches together. Two systems of these are 

 present, one of which is dorsal (ia.d.'^~^) and the other 

 lateral {ia.l}'^) in position. The dorsal interarcuales 

 consist of bands which bind the pharyngobranehial car- 

 tilages together. In Heptanchus maculatus the first or 

 anterior interarcualis is large and extends from the first 

 to the second pharyngobranehial cartilage. The follow- 

 ing dorsal interarcuales decrease in size and bridge suc- 

 ceeding pharyngobranchials. 



There is present in Heptanchus the so-called sub- 

 spinalis {s.sp., fig. 94) which, unlike the dorsal inter- 

 arcuales, takes its origin from the posterior part of the cranium, from the 

 spinal column, and from the ventral fascia of the longitudinal bundle. Like 

 the dorsal interarcuales it is inserted on pharj^ngobranchial cartilages, but, 

 unlike them, it is inserted bj^ a double tendon on the tips of the first and second 

 pharyngobranchials. 



The lateral interarcuales {ia.L, fig. 94), except the sixth {ia.lS'), are double 

 bands, the anterior of which in eacli pair bridges the angle between pharyngo- 

 branehial and epibranchial cartilage of the single arch; while the posterior one 

 extends from the following pharyngobranehial to a common insertion with 

 the anterior muscle on the upper and posterior surface of the epibranchial. 



rig. 93. The ventral 

 constrictors, Heptan- 

 cJius cinereiis. (From 

 Vetter. ) 



csr.^"^"*, first, second, 

 and eighth ventral con- 

 strictor muscles. 



