102 



THE ELASMOBRANCH FISHES 



In the rays, the fibers of the dorsal constrictors are not continuous with those 

 of the ventral constrictors, the two sets being separated by a horizontal tendon. 



DOESAL CONSTRICTORS 



The first dorsal constrictor in Acanthias (fig. 104), as has been said, is sepa- 

 rated from the levator maxillae only at the ventral part of the spiracle where 

 its fibers curve posteriorly around the base of the spiracle to be attached to 



Fig. 104. Lateral pharyngeal muscles, Acanthias. (From Vetter.) 



a.md., adductor mandibulae ; csd.-, second dorsal constrictor ; csv., ventral constrictor ; 

 Us., levator labii superioris ; \.mx., levator maxillae ; tr., trapezius. 



the quadrate. In a boiled specimen of Mu^telus californicus the first dorsal 

 constrictor can readily be distinguished from the levator maxillae by a differ- 

 ence in its color. Furthermore its anterior ventral margin folds in under the 

 levator maxillae. In the rays (fig. 105) the first dorsal constrictor is a clearly 

 marked band which forms a crescent in front of the spiracle. 



In Elasmobranchs which have a nictitating membrane the muscles con- 

 trolling that membrane are derivatives of the first dorsal constrictor. The nic- 

 titator in Mnsielus californicus may here be described with the other accom- 

 panying muscular slips. It has its origin posterior to that of the first dorsal 

 constrictor and under the second dorsal constrictor. From its origin it passes 

 anteriorly and downward in front of the spiracle {nt., fig. 106) to be inserted 

 on the nictitating membrane (tj.). Crossing the nictitator almost at right 

 angles is a deeper muscle, the depressor (dp.) of the upper eyelid, which takes 

 origin somewhat posterior and dorsal to the spiracle and over the second con- 

 strictor. This passes forward and upward to be inserted at the tail of the eye 

 on the upper eyelid. Arising in the common mass with the depressor of the 

 upper lid but superficially, is a rudimentary retractor palpebrae superioris 

 (r.p.) which ends anteriorly against the nictitator so that the nictitator oper- 

 ates between it and the depressor. Arising from the anterodorsal margin of 



