50 CESTRACIONTS. 



usual position of the jaws in the osseous fishes. In consequence also 

 of the greater extent of ossification in these parts, the indications of 

 the separation of the upper jaw into maxillary and premaxillary, and 

 of the lower jaw into mandibular and premandibular pieces begin to 

 be visible. The upper jaw, besides being suspended to the tympanic 

 or articular pedicle, is articulated by a distinct convex process with 

 a corresponding concavity on each side of the vomerine portion of 

 the cranium. A similar connection of the upper maxillary bone, 

 in the Scarus, illustrates the analogy here advanced between the upper 

 dentigerous arch in the Cestracion and other Plagiostomes and the 

 ordinary maxillary and intermaxillary bones. This arch is also 

 attached by ligamentous matter, as in other sharks, to the frontal and 

 nasal parts of the cranium, with which it is in contact. The maxil- 

 lary portion of the upper jaw sends outwards a strong process which 

 is connected with a corresponding external process of the lower jaw, 

 and a very strong ligament attaches the inner side of the posterior 

 extremity of the superior maxillary bone to the inner side of the 

 broad transverse condyloid extremity of the lower jaw. The inter- 

 space of the upper maxillary bones is occupied by a thin triangular 

 plate of cartilage representing the matrix in which, in osseous fishes, the 

 palatine bones are developed, and two lateral posterior processes of this 

 cartilage which abut against the tympanic pedicle, represent the trans- 

 verse and pterygoid bones. 



The labial cartilages, regarded by Cuvier in the Squatina and 

 some other Plagiostomes as the rudimental and toothless represen- 

 tatives of the maxillary, intermaxillary, and premandibular bones, 

 and which in the Cestracion might have been expected, in harmony 

 with the general tendency of its cranial structure, to have been 

 present with a corresponding advance towards their hypothetical 

 maxillary character, have, on the contrary, totally disappeared. 



The lower jaw, consisting of the articular and premandibular 

 elements still confluent, is suspended partly to the slender tympanic 

 pedicle, but principally to the expanded posterior extremity of the 

 superior maxillary bone. It closely resembles the upper jaw in form, 

 but is of greater depth, and the symphysis, which is never obliterated, 

 is of greater breadth, and is terminated more squarely. 



The teeth are arranged, as in the Plagiostomes generally, in 



