640 PISCES. 



of the abdomen to the tail, which latter holds the same position as in 

 other tribes : so that the reader will have little difficulty in comparing 

 the different pieces of the skeleton of the Flounder (Pleuronectesflesus) 

 with the corresponding bones of the Perch already described. 



(1740.) The skeletons of the cartilaginous fishes (Chondropterygii*} 

 will require a distinct notice, inasmuch as they present very remarkable 

 peculiarities of no inconsiderable interest. In the Sharks, Skates, and 

 other genera belonging to this important division of the great class we 

 are now considering, the interior of the bones remains permanently 

 cartilaginous ; but the skeleton is in some regions incrusted, as it were, 

 with osseous granules. No centres of ossification from which radiating 

 fibres of bony matter progressively extend themselves, as is the case in 

 the osseous fishes, are ever developed; and consequently the skull, 

 although it presents externally the same regions, eminences, and aper- 

 tures that are usually met with, is never divided into separate bones, 

 but is formed of a single mass of cartilage, in which no sutures or lines 

 of division are ever distinguishable. 



(1741.) The face is likewise much more simple in its structure; for, 

 instead of the numerous pieces composing the palato-temporal region 

 of the Perch ( 1714), two bones only are met with, one of which, the 

 palatine, performs the office of an upper jaw and supports the teeth, 

 while the other connects the lower jaw with the cranium. The lower 

 jaw itself, moreover, consists of but one piece on each side, to which the 

 teeth are attached. 



(1742.) From the peculiar conformation of the respiratory apparatus, 

 which will be explained hereafter, there is no occasion for any oper- 

 cular flap ; this, therefore, is not present : nevertheless the hyoid and 

 branchial arches resemble pretty much those of osseous fishes ; only the 

 latter are situated further backwards, being placed quite behind the 

 skull, under the commencement of the spine. 



(1743.) The bones of the shoulder are represented by a strong carti- 

 laginous zone, which in Sharks is quite unconnected with the vertebral 

 column, but in the Skate (Raia) it is fixed to two large lateral apophyses 

 derived from the spine (fig. 316). The zone, representing the scapulary 

 apparatus, consists of a single piece, which surrounds the body, and on 

 each side supports the bones of the fore-arm. The enormously- deve- 

 loped pectoral fin is composed of the carpus, amazingly augmented in 

 size, and of the no less remarkable hand, which in the Skate is made up 

 of an immense number of fingers or rays, and forms by itself nearly 

 half the circumference of the body. 



(1744.) The pelvis, or cartilaginous framework that supports the 



hinder extremities, i. e. the ventral fins, is a single transverse piece of 



cartilage quite detached from the rest of the skeleton : it expands on 



each side into a broad plate, to which the fin, the representative of the 



* Xovdpos, cartilage; irrepvyiov, a fin. 



