THE SKULL OF ACANTHIAS VULGARIS 433 



meet the second hypobranchials on their lateral (posterior) 

 sides, and also they articulate with the second basibranchial. 



The fifth ceratobranchial is wider than its fellows and bears 

 plate-like expansion, directed laterally, on its posterior bor- 

 der, while anteriorly there is a strong process or tubercle. This 

 arch lacks a hypobranchial, the ceratobranchial articulating 

 directly with the second basibranchial. 



The second basibranchial is a flattened triangular plate of 

 cartilage, the apex of the triangle directed posteriorly. At 

 about two-thirds the distance towards the posterior angle, it is 

 slightly constricted, and from this line a shallow groove runs for- 

 ward in the median line of the dorsal surface. 



Thin plates of cartilage, the extra-branchials occur on the 

 outer sides of the gill arches. Of these there are two series, a 

 dorsal and a ventral, the former parallel with the epibranchial 

 elements, the ventral bearing the same relations to the cerato- 

 branchials. These occur in each arch, but the anterior extra- 

 branchials are so small that they may easily be overlooked. 

 These cartilages serve as points of attachment for the posterior 

 four dorsal constrictor muscles. 



The regions of muscular attachment on the visceral skeleton 

 are somewhat numerous. The adductor mandibulae (fig. 5, am.) 

 has its origin from the quadrate portion of the pterygoquadrate 

 bar; it extends ventrally and posteriorly and, then, curving for- 

 ward, is inserted on the depressed posterior external surface 

 of Meckel's cartilage. The first constrictor superior dorsalis 

 (csd. 1) is inserted on the more medial region of the hyoman- 

 dibular, while the anterior fibers of the second (csd. 2) are in- 

 serted on it, near its articulation with the ceratohyal. (These 

 were described as attached to the upper jaw by Marion, but 

 this was not the case in the specimen I examined.) Other more 

 lateral fibers of this muscle are inserted on the posterior edge 

 of the ceratohyal. The first constrictor superior ventralis 

 (csv.l.) is inserted along the postero-ventral margin of Meckel's 

 cartilage, while the second, (csv. 2.) has its insertion on the 

 ventral edge of the ceratohyal. The levator maxillae superioris 

 (Ims.) is inserted on the pterygoquadrate bar of either side, 



