94 



THE ELASMOBRANCH FISHES 



inserted at the symphysis of the mandible. The paired coracohyoideus muscles 

 {c.hy.) continue forward from the coraeoarcuales as a layer just dorsal to the 

 sides of the coracomandibularis. They are relatively broad muscles in Hep- 

 tanchus and are inserted on the basi- and ceratohyoid cartilages {ch., fig. 50a) , 

 only a few of the fibers reaching the base of the ceratohyoid cartilage. Dorsal 



to the region of the coraco- 

 hyoideus muscle is the third 

 group, the coracobranchi- 

 ales muscles (c.6r.^""). The 

 first six of these arise from 

 the heavy connective tissue 

 dorsal to the coraeoarcuales 

 and pass forward, upward, 

 and outward as narrow slips 

 to be inserted on the hypo- 

 branchial cartilages. The 

 last or seventh (c.hr.~) arises 

 in two parts; one part is 

 continuous with the sixth, 

 and the other originates di- 

 rectly from the coracoid 

 cartilage. This muscle in- 

 serts as a wide band along 

 the whole length of the last 

 ceratobranchial cartilage 

 and a part of the median 

 piece. Slips of the ventral 

 constrictor ( interbranchial, 

 ihv.^'''\ fig. 95) muscles pass 

 through the ceratobranchial 

 muscles. 



Muscles op the Fins 



Fig. 95. Ventral longitudinal or hypobranehial muscles, 

 Heptanchus maculatus. (From Davidson.) 



hh., basihyal cartilage ; car., coracoarcualis muscle ; 

 c&.\ first ceratobranchial cartilage ; c.hr}'', first to 

 seventh coracobranchial muscles ; ch., ceratohyal carti- 

 lage ; c.hy., coracohyoideus; c.md., coracomandibularis 

 muscle; co., coracoid cartilage; rbv.^"", first to sixth in- 

 terbranchial slips; md., mandibular cartilage. 



The muscles on the dorsal 

 side of the pectoral fin 

 (d.r.m., fig. 90) take origin 

 from the posterolateral 

 margin of the scapula, and from the basal and, in part, from the radial car- 

 tilages of the fin skeleton. The radial muscles are distinct in the central part of 

 the fin, but on the posterior margin the separation into definite bundles is not 

 so evident. The muscles run toward and are attached to the heavy sheet of 

 connective tissue continuous with the dermal fin-rays (d.f.). The radials 

 while appearing to be long are, according to Davidson, made up of short fibers. 

 The ventral radial muscles arise from the posterior side of the coracoid and 



