154 JJnivcrsitij of California PuhUcations in Zoology [^^o-l. is 



and ventral part. This division, however, is not a natural one for the 

 fibers, except in the ease of the first and second divisions, are con- 

 tinuous from the dorsal to the ventral part. 



Dorsal constrictors {csd. ^■^). The dorsal constrictors have a con- 

 tinuous origin extending from the cranium, just back of the postor- 

 bital process, to the pectoral girdle. The anterior part of the origin 

 is from the cranium, but the main part is from the sheath of connective 

 tissue which covers the trapezius and dorsal longitudinal muscles of 

 the pharyngeal region. 



The first dorsal constrictor (csd. \ fig. 1) is continuous with the 

 levator maxillae superioris, but the fibers of the two have a different 

 direction. Its anterior extent is diffcult to determine in Heptanchus 

 maculatus, but it is limited posteriorly by the spiracle. Its origin is 

 on the cranium posterior to the origin of the levator maxillae supe- 

 rioris, and in the connective tissue described above. The fibers of the 

 first dorsal constrictor are slightly shorter than those of the levator. 

 It is inserted along the dorsal edge of the quadrate posterior to, and 

 continuous with the insertion of the levator maxillae superioris. The 

 two muscles function together in raising the jaw and constricting the 

 spiracle. 



The second dorsal constrictor {csd. -) is the largest of the dorsal 

 series. It lies between the spiracle and the first gill-slit. Its origin 

 is continuous with that of the first dorsal constrictor. The anterior 

 deeper part is inserted on the middle of the dorsal segment of the 

 hyoid arch. The main part of the muscle is inserted dorsally on the 

 palatoquadrate from the insertion of the first of this series to the 

 angle of the jaws. The fibers between the angle and the gill-slit are 

 continuous with those of the corresponding part of the ventral series. 

 In passing over the median cartilaginous rays the fibers become 

 tendinous. 



Dorscd constrictors"'^ have a similar origin and extent. They de- 

 crease in size posteriorly corresponding to the decrease in size of the 

 branchial apertures. Their origin is continuous in the connective 

 tissue sheath of the trapezius. Their fibres run ventrally and are 

 continuous with those of the corresponding ventral constrictors. 



Ventral constrictors (csv. -■*, fig. 1). There is a difference of 

 opinion concerning the naming of the ventral constrictors. Vetter 

 (1874, pp. 409-416) describes them for both Acanthias and Hep- 

 tanchus and does not recognize a first ventral constrictor in either 

 form. Marion (1905, pp. 7-8), although saying nothing of Heptan- 



