1918] Davidson: The Musculatnir of HfpfaNchus niacnlatus 153 



primitive characteristics. They are concerned chiefly 

 and food getting, and include the following groups : 

 I. Superficial circular muscles. 

 II. Interarcuales. 



III. Subspinalis. 



IV. Adductors. 



V. Hypobranchials. 

 I. The Superficial Circular Muscles (fig. 1). 

 circular muscles form an almost complete muscular 

 pharyngeal region. In general they are thin and 

 running around the pharynx. The function of this g 

 is to constrict the pharynx and close the gill-clefts, 

 of muscles are included in this division, some of which 

 connected in origin, insertion, and function. 



csd.' csd.'* 



with respiration 



The superficial 

 covering of the 

 flat with fibers 

 roup of muscles 

 Several series 

 are very closely 



CSV. 



Fig. 1. Head of Ueptanchus niaculatus, lateral view (X %). a. md., adductor 

 mandibulae; a. pr., antorbltal process; c.sd.^-*, first to eighth dorsal constrictors; 

 Us.^'- first and second parts of levator labialis superioris; hmx., levator maxillae 

 superioris; md., mandible; po. o., postorbital process; p-q., palatoquadrate car- 

 tilage; sc. scapula; sp., spiracle; //•.. trapezius. 



1. Levator maxillae superioris {I. mx., fig. 1). The levator maxil- 

 lae superioris is described first in this group as it seems to be an 

 anterior continuation of the dorsal constrictors, and to share their 

 function. It consists of a group of short fibers having its origin under 

 the supraotic crest just posterior to the postorbital process. Its direc- 

 tion is ventral and anterior and it is inserted on the anterior and 

 dorsal edge of the enlarged quadrate region of the upper jaw just 

 anterior and continuous with the insertion of the first dorsal con- 

 strictor. Its function is to raise the upper jaw. 



2. Superficial constrictors. The superficial constrictors form a 

 thill muscular layer almost completely covering the branchial region. 

 This group is divided for convenience of description into a dorsal 



