156 University of California Pi(bUcatio)is in Zoology [Vol.18 



sides have their origin from a band of connective tissue extending 

 from the pectoral girdle to the mandibular symphysis. It is broad 

 near the girdle but narrows rapidly forming a triangular ventral 

 covering for the coaracoarcuales communes. From this it continues 

 forward as a narrow strip from which the anterior part of the second 

 ventral constrictor takes its origin. Anteriorly this muscle is covered 

 by the first ventral constrictor, a thin layer of fibers lying directly 

 under the skin and being continuous from one ramus of the mandible 

 to the other. This, the first ventral constrictor, cannot be clearly 

 separated from the second. It is inserted on the inner side of the 

 ramus of the mandible. The anterior part of the second dorsal con- 

 strictor is inserted along the middle third of the ceratohyoid cartilage ; 

 the posterior part is continuous with the corresponding dorsal con- 

 strictor. In passing over the median cartilaginous branchial rays 

 the muscle forms a tendinous aponeurosis. 



Ventral constrictors^''^ {csv.'^'^) have their origins continuously 

 along the edge of the triangular piece of connective tissue which 

 covers the coracoarcuales communes. They pass between the gill- 

 slits and continue as the fibers of the corresponding dorsal parts. 



3. Interhranchials. The interbranchial muscles are so intimately 

 connected with the dorsal and ventral constrictors that they are in 

 fact parts of the same muscles. The fibers {ihd., fig. 2) are parallel 

 with and anteriorly continuous with the constrictors (csd.), and lie 

 just in front of and against the cartilaginous branchial rays. They 

 are present in the six holobranehs, but an interbranchial is absent from 

 the hyoidean demibranch. Their function is to draw the branchial 

 rays together and constrict the gill-pockets. 



For convenience of description they may be divided into dorsal 

 and ventral parts, corresponding to the constrictors which have been 

 similarly grouped. The origin of the dorsal parts is in the connective 

 tissue of the trapezius and dorsal longitudinal muscles anteriorly con- 

 tinuous with the origin of the corresponding dorsal constrictors. They 

 are attached to the dorsal extrabranchial cartilages which serve to 

 hold the muscles in place. The anterior fibers are inserted along the 

 entire dorsal edge of the epibranchial cartilage from the insertion of 

 the lateral interarcuales to the angle between the epibranchial and 

 ceratobranchial segments of the branchial arches. The outer or more 

 posterior fibers continue into the corresponding ventral part. The 

 ventral parts (i&t'.^"*"', fig. 4) have their origin in the connective tissue 

 dorsal and lateral to the coracoarcuales communes. The posterior 



