1918] Davidson: The Musculature ejf Hrptaiiclnts maculatus 159 



single head from the dorsal end of the seventh epibranehial, and from 

 the sixth phar.yngobranchial as in the case of the others of the series. 

 The two cartilages are closely articulated by connective tissue and 

 the origin of this muscle is continuous. The insertion is on the sixth 

 epibranehial as in the case of the others of this series. 



III. SuBSPiNALis {s. sp., fig. 3). Anterior to each series of dorsal 

 interarcuales is a single muscle, the subspinalis (Vetter, 1874, p. 444). 

 Marion (1905, p. 24) in disagreement with Vetter who considers this 

 muscle as belonging to a distinct group, considers it as the most ante- 

 rior dorsal interarcualis. Its origin, insertion, and occurrence, how- 

 ever, do not agree with the dorsal interarcual series and it seems advis- 

 able here to describe it separately as the subspinalis muscle. 



It has a broad origin ventrally from the posterior part of the 

 cranium, the vertebral column near the cranium and from the ventral 

 fascia of the dorsal longitudinal muscles. It decreases in size abruptly 

 and is inserted by two tendons, the larger on the median end of the 

 first pharyngobranchial dorsally, and the smaller similarly on the 

 second. 



IV. Additctors. The adductors form a series of flexors for the 

 dorsal and ventral parts of the visceral arches, except in case of 

 the hyoid, on wliich the muscle is lacking. This is probably due to the 

 reduction of the hyoid arch and to its dependence on the first or mandi- 

 bular arch. These muscles are very small except in the case of the first 

 which in correlation with the great use of the mandibular arch is 

 enormously developed. 



1. Adductor mcuidihulae. The adductor mandibulae (a. md., fig. 

 1), the adductor of the first visceral arch, is very much larger and 

 more specialized than the other members of this series. It appears 

 as a simple muscle having its origin externally on the quadrate region 

 of the upper jaw, and its insertion similarly on the mandible. This is 

 the case, however, with only a small part of the muscle, the deeper 

 posterior part which comprises less than one-third of the whole muscle. 

 This small part corresponds closely to the adductors of the succeeding 

 arches. The posterior superficial fibers have their origin on the quad- 

 rate, but insert on the tendinous envelope covering the ventral part 

 of the adductor. The remainder, which is by far the greater part of 

 the muscle, is divided into dorsal and ventral parts by the membranous 

 posterior continuation of the first part of the levator labialis superioris. 

 The dorsal division has its origin on the quadrate portion of the upper 

 jaw; its direction is ventral and slightly anterior, and its insertion is 



