104 



THE ELASMOBRANCH FISHES 



(Acanthias), the fibers dorsally arise largely from the seam above the cleft 

 and from the extrabranchial cartilages. These fibers pass do^\^lward and 

 those more anterior are inserted on the seam in front and on its underlying 

 extrabranchial cartilage (fig. 104). The posterior fibers pass on and are con- 

 tinuous with the ventral constrictors. The sixth dorsal constrictor in addition 

 has some of its fibers arising from the scapular part of the pectoral girdle. 



In the rays there is present a levator rostri (l.r., fig. 105). This muscle has 

 its origin dorsally in the fascia of the longitudinal muscle, near the posterior 



seam at the sides of the dorsal con- 

 strictor, and extends to the margin of 

 the rostrum (Rhinohatis) where it is 

 inserted on heavy tissue. 



The trapezius, which is not a part of 

 the constrictor system, may here be 

 considered. In sharks it arises from the 

 fascia of the dorsal bundles, and from 

 the cranium above and at the sides of 

 tlie ninth foramen (Acanthias), its 

 origin extending almost from the cra- 

 nium to the region of the scapula. In 

 Acanthias (#r., fig. 104) it is perforated 

 by slips of the dorsal constrictors and 

 has its insertion largely on the scapula. 

 In the rays several slips of muscle are 

 found in the location of the trapezius, 

 but it is not certain that these are comparable with the trapezius of the sharks. 



Fig. 106. Muscles to the nictitating mem- 

 brane and associated parts, lateral view, 

 Mustelus calif ornicus. 



C.S., constrictor spiraculae; dl., dilator 

 spiraculae; dp., depressor of upper lid; 

 I., upper eyelid ; n., nictitating membrane ; 

 ?i^.,nictitator muscle ; r.p., superficial fibers 

 which do not reach upper lid ; sp., spiracle. 



VENTEAL CONSTRICTOES 



In Acanthias, according to Marion (1905) there may be two parts to the first 

 ventral constrictor, the more anterior of which is the smaller and bridges the 

 anterior symphysis of the lower jaw. The more posterior part is much wider 

 and is like that in Heptanchus. These parts take origin from a midventral 

 seam and are inserted on the posterior margin of the mandible. In the rays the 

 second part acts as a depressor mandibulae {cl.mcl., fig. 107b). 



The second ventral constrictor in the sharks is similar to that in Heptanch lis. 

 This also arises from the midventral seam and is inserted on the border of the 

 hyoid cartilage. In the rays the second ventral constrictor is divided into an 

 anterior and a posterior part. The anterior part acts as a depressor hyomandib- 

 idaris {d.hm., fig. 107b) , a muscle antagonistic to the levator hyomandibularis 

 previously mentioned as derived from the second dorsal constrictor. The more 

 posterior and narrower ventral part is the second ventral constrictor. 



Each of the remaining ventral constrictors in the rays (fig. 107b) consists 

 of two parts, a large outer and a small inner portion. 



