218 VERTEBRATE ANIMALS. 



monly known as the " bony " fishes. In all the Teleostei, the 

 skeleton is bony, the skull is composed of distinct bones, and 

 there is a lower jaw. The vertebral column always consists 

 of more or less completely ossified vertebras; and the two 

 pairs of limbs, when present, are in the form of fins, supported 

 by rays. The gills are free, comb-like or tufted in shape, and 

 always protected by a bony gill-cover. The bulbus arteriosus 

 is not capable of regular contractions, and is separated from 

 the ventricle by only a single valve. 



The order Teleostei comprises almost all the most familiar 

 fishes, and it will be unnecessary to dilate here upon their 

 structure, as they were taken as the type of the class in de- 

 scribing the fishes generally. It may be as well, however, to 

 recapitulate some of the leading points in the anatomy of the 

 bony fishes. 1. The skeleton is always more or less complete- 

 ly ossified, and does not remain cartilaginous throughout life. 

 The notochord is not permanent, and the vertebral column 

 consists of a number of distinct vertebras. The vertebras, 

 however, are " amphiccelous," or hollow at both ends, so that 

 there is left between each pair a doubly-conical cavity, which 

 is filled with the cartilaginous or semi-gelatinous remains of 

 the notochord. In this way an extraordinary amount of flexi- 

 bility is given to the entire vertebral column. In no fish (ex- 

 cept the Bony Pike, which belongs to another order) is the 

 conversion of the bodies of the vertebras into bone carried 

 further than this. 



2. The integument usually develops scales, and these in 

 the great majority of cases are of the forms known as " cy- 

 cloid " and " ctenoid," the former being circular or elliptical 

 horny plates, with plain margins ; while the latter have their 

 hinder margins cut into comb-like projections, or fringed with 

 spines (Fig. 100, a, b). 



3. The anterior and posterior limbs are usually, but not 

 always, present, and when developed they are always in the 

 form of tins. These fins may be supported by " spinous rays " 

 or " soft rays," or by both. . The spinous rays are simple un- 

 divided bony spines which taper to a point. The soft rays 

 are doubly divided, splitting up toward their extremities into 

 a number of secondary rays, and being also divided by trans- 

 verse joints into numerous short pieces. 



4. Besides the " paired " fins which represent the limbs, 

 there is also a series of unpaired or " median " fins, the rays 

 of which are supported upon a series of dagger-shaped bones, 

 deeply plunged in the flesh in the middle line of the body, 



