THE ELASMOBRANCn FISHES 



103 



the spiracle is the dilator {(U.) of tlie spiracle, which passes anteriorly and nj)- 

 ward between the reti-actor and dej)ressor finally to join the nictitator. Sur- 

 rounding the spiracle (sp.) sui)erficially is the constrictor spiraculae (c.s.). 

 The second dorsal constrictor (cs(]r, fig. 104) in the sharks extends from the 

 supraotic crest of the cranium back to and even perforating the anterior end 

 of the trapezius (tr.) ; other fibers arise from the seam dorsal to the cleft. The 



a.md. 



A B 



Fig. 105. Dorsal pharyngeal muscles. (Prom Tiesing.) A. Torpedo. B. Baja. 



a.md., adductor mandibulae; csd., dorsal constrictor muscle; l.hm., levator hyoman- 

 dibularis; lls.'^-', first to fifth slips of levator labiales; l.mx., levator maxillae; /.r., levator 

 rostri. 



insertion of this muscle in Acanthias is interesting. Part of its fibers touch the 

 hyomandibula and a number of other fibers impinge on the ceratohyoid ; while 

 still a third set joins a horizontal tendinous bridge, separating dorsal and 

 ventral constrictors. Back of this tendon other fibers are continuous with the 

 ventral constrictors. 



Those fibers inserted on the hyoid in Heterodontus and Squatina are sepa- 

 rated into a kind of levator hyomandibularis. In the rays the levator hyo- 

 mandibularis (l.hm., fig. 105) is a muscle of great importance. It may be in- 

 serted on the hyomandibula at the angle {Torpedo, fig. 105a, l.hm.; Raja (fig. 

 105b) , or on the lower part as in Rhinohatis. In the rays those fibers back of the 

 levator hyomandibularis and in front of the first cleft form the second dorsal 

 constrictor proper. These fibers run practically in a horizontal direction. 



The remaining dorsal constrictors are similar to the second. A point or two, 

 however, may be added. From the third to the fifth constrictors in the sharks 



