152 University of California Publications in Zoology [Vol.18 



seven large gill-slits which decrease in size posteriorly. It is a large 

 form, some of the specimens taken having reached nine feet in length. 

 For the greater part of this study small specimens of about two to three 

 feet in length were used. This work was suggested by Professor J. 

 Frank Daniel, to whom the author is indebted for assistance and 

 criticism. 



Historical 



The literature on the pharyngeal musculature of elasmobranchs 

 is scanty. Vetter (1874) described the pharyngeal musculature of 

 Heptanchus cinereus, Acanthias vulgaris, and Scymnus licJiia. Ties- 

 ing (1896) published a paper on the musculature of the rays. Marion 

 (1905) wrote a paper on Acanthias vulgaris and the skate, Raia 

 erinacea, in which he drew comparisons between the musculature of 

 sharks and rays. Tiesing classified muscles on the basis of ennervation 

 and this is perhaps the most reliable single criterion although it has 

 its disadvantages. Vetter and Marion used position and function, 

 which plan is followed in this paper. 



This work agrees as a whole with previous publications although 

 slightly different interpretations are offered in a few instances. The 

 various organs of Heptanchus seem to agree remarkably well with 

 those of Hexanchus griseus as described by Ruge (1897) in an article 

 on the facial nerve in vertebrates. There are many articles on the 

 paired fins of selachians, but these deal mainly with their origin and 

 relation to the paired limbs of the higher vertebrates. The papers of 

 Krall (1908), Goodrich (1906), and Erik Miiller (1909) have been 

 particularly helpful. The bibliography on the body musculature is 

 large, but several of the more important articles, including those of 

 Johannes Miiller and A. Schneider, have not been available. 



THE MUSCULATURE 



The musculature may be divided as follows : 



Pharyngeal musculature. 

 , Musculature associated with the organs of special sense. 



Appendicular musculature. 



Musculature of the trunk. 



Pharyngeal Musculature 

 This group includes the muscles anterior to the pectoral girdle. 

 These muscles are very much specialized, but still retain some of their 



