358 MANUAL OF ZOOLOGY. 



and it corresponds very nearly with Cuvier's division of the 

 " osseous" fishes. The Teleostei are defined as follows : The 

 skeleton is usually well ossified ; the cranium is provided with 

 cranial bones ; and a mandible is present ; whilst the vertebral 

 column almost always consists of more or less completely ossi- 

 fied vertebrae. The pectoral arch has a clavicle ; and the two 

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

 by rays. The gills are free, pectinated or tufted in shape ; a 

 bony gill-cover and branchiostegal rays being always devel- 

 oped. The branchial artery has its base developed into a bul- 

 bus arteriosus ; but this is never rhythmically contractile, and 

 is separated from the ventricle by no more than a single row 

 of valves. 



The order Teleostei comprises almost all the common fishes ; 

 and it will be unnecessary to dilate upon their structure, as 

 they were taken as the types of the class in giving a general 

 description of the Fishes. It may be as well, however, to 

 recapitulate very briefly some of the leading characters of the 

 order. 



I. The skeleton, instead of remaining throughout life more 

 or less completely cartilaginous, is now always more or less 

 thoroughly ossified. The notochord is not persistent, and the 

 vertebral column, though sometimes cartilaginous, consists of a 

 number of vertebrae. The bodies of the vertebrae are what is 

 called "amphicoelous" that is to say, they are concave at 

 both ends. It follows from this, that between each pair of 

 vertebrae there is formed a doubly-conical cavity, and this is 

 filled with the cartilaginous or semi-gelatinous remains of the 

 notochord. By this means an extraordinary amount of flexi- 

 bility is given to the entire vertebral column. In no fish except 

 the Bony Pike (which belongs to the order Ganoidei) is the 

 ossification of the vertebral centra carried further than this. 

 The skull is of an extremely complicated nature, being com- 

 posed of a number of distinct cranial bones ; and a mandible 

 or lower jaw is invariably present. 



II. The anterior and posterior pairs of limbs are usually, but 

 not always, present, and when developed they are always in 

 the form of fins. The fins may be supported by " spinous" or 

 " soft" rays, of which the former are simple undivided spines 

 of bone, whilst the latter are divided transversely into a num- 

 ber of short transverse pieces, and also are broken up into a 

 number of longitudinal rays proceeding from a common root. 

 (The Fishes with soft rays in their paired fins are termed 

 " Malacopterygii" those with spinous rays, " Acant/wpterygii") 



III. Besides the paired fins, representing the limbs, there is 



