64 ANNALS NEW YORK ACADEMY OF SCIENCES 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Constrictor 2 superficial dorsalis (C 2 md, Ruge; Csd 2 , Marion). 

 Coracomandibularis (Co. m.). 

 Coracohyoideus (Co. hy.). 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V 3 ) 



Adductor mandibular (Adm.). — This is the large adductor muscle of 

 the shark which closes the mandible against the maxillary or palato- 

 quadrate bar. It lies on the skull, anterior to the hyomandibular, and 

 fills the lower part of the space between this and the eye. It arises along 

 the dorsal margin of the quadrate. A superficial layer arises on the post- 

 orbital process and some of the fibers come from the tendinous mass back 

 of the eye. At the postero-ventral region a few of the fibers from C^v 

 join with the adductor. The insertion is on the cartilage of the mandible 

 along the whole length of the exterior surface and slightly on the upper 

 edge of the inner surface. A tendon extends to the levator labii superioris 

 (L. 1. s.) somewhat as it does in the teleosts, where a tendon connects 

 with the adductor from the premaxillary region of the skull. Marion 

 (1905, p. 23) gives a similar muscle in Raia which he calls levator rostri. 



In Acanthias the adductor muscle is a large mass made up of fibers 

 from several sources, as in the teleosts and ganoids. It is more divided 

 and specialized in Raia than in the typical sharks. The typical condition 

 of this muscle in the lowest forms shows fibers from several sources, and 

 this is suggestive of the subdivisions of the mucle in the higher forms, 

 where the same mass in the amphibians and reptiles is divided to a greater 

 or less extent, according to the form of the animal and the type of jaws. 

 Tiesing (1895, pp. 87-90) discusses the adductors of the various elasmo- 

 branchs, showing this splitting of the muscle in some of them, especially 

 Rhinobatus. 



Levator labii superioris (L. 1. s.) is a small muscle arising on the ven- 

 tral portion of the skull, under the eyes and anterior to them, extending 

 around the labial cartilages to meet and join with the adductor man- 

 dibulae. 



Vetter (1874, p. 406) calls it Add. (3 in Acanthias and places it with 

 the "Oberflachliche Ringmuskulatur" (Constrictor arcuum visceralium). 

 Marion (1905, p. 21) follows Vetter and places it with the similar con- 

 strictor, as a serial homologue ' of the M. levator maxillae superioris. 

 Tiesing (1895, p. 84) gives the origin in Mustelus "von vorderer Wand 



