238 FISHES. 



happens that moveable articulations, which are found in other orders, are 

 not met with in this one; part of the vertebras of certain Rays, for in- 

 stance, being united in a single body; some of the articulations of the 

 bones of the face also disappear, and the most apparent character of this 

 division consists in the absence of the maxillaries and intermaxillaries, or 

 rather in their reduction to mere vestiges concealed under the skin, while 

 their functions are fulfilled by bones analogous to the palatines, and even 

 sometimes by the vomer. The gelatinous substance, which in other fishes 

 fills the intervals of the vertebras, and only communicates with them by a 

 small hole, forms a long cord in several of the Chondropterygians, which 

 traverses the bodies of almost all the vertebrae, without scarcely varying in 

 diameter. 



This series is divided into two orders — the Chondropterygians, whose 

 branchiae are free, like those of ordinary fishes, and those in which 

 they are fixed, that is to say, attached to the skin by their external edge 

 in such a manner that the water can only escape from their intervals 

 through holes on the surface. 



The first order of Chondropterygians, or the seventh of the class of 



Fishes : 



ORDER I. 



THE STURIONES, or CHONDROPTERYGIANS WITH 

 FREE GILLS. 



The Fishes of this order are still closely allied to the ordinary fishes in 

 their gills, which have but a single wide opening, and are furnished with 

 an operculum, but without rays in the membrane. It comprises but two 

 genera. 



Acipenser*, Lin, 



The general form of the Sturgeon is similar to that of the Shark, but 

 the body is more or less covered with bony plates in longitudinal rows; 

 the exterior portion of the head is also well mailed; the mouth, placed 

 under the snout, is small and edentated; the palatine, soldered to the 

 maxillaries, converts them into the upper jaw, and vestiges of the inter- 

 maxillaries are found in the thickness of the lips. This mouth, placed on 

 a pedicle that has three articulations, is more protractile than that of the 

 Shark. The eyes and nostrils are on the side of the head, and cirri are 

 inserted under the snout. The labyrinth is perfectly formed in the cra- 

 nial bone, but there is no vestige of an external ear. A hole perforated 

 behind the temple is a mere spiracle, which leads to the branchiae. The 



* Aclpensi'r is the anticnt name; Sfurio,- whence Sturgeon, is modern, and Is pro- 

 l):il>l\ theGerman name Sloer latinized. 



