Class 2. Pisces. 



367 



arched bone, the clavicle. This series of bones is fastened above 

 to the hinder end of the skull. In the Ohondrostei the cartilage of 

 the shoulder girdle is always very well developed in spite of the 

 presence of membrane bones ; in the Holostei, and the Teleostei, the 

 original part of the shoulder girdle is usually much reduced in size, 

 and is represented only by a small plate, attached to each clavicle. 

 In the Teleosteans two ossifications are present in this plate, the 

 scapula and ooracoid. In the Dipnoi relations similar to 

 those of the Ohondrostei obtain. The skeleton of the fore limb 

 consists, in the Selachians, of a number of flattened cartilages: 

 at the base of the limb are three large ones articulated to the 

 shoulder girdle, the b a s a 1 i a, and to the edge of these is attached a 

 larger number of jointed cartilaginous rays, the radialia. These 

 lie close together in the Sharks, but in the Eays, where they are very 

 long, they are somewhat further apart. In the Ganoids this 

 skeleton is reduced in size, the radialia are shorter, the basalia 



Fig. 304. Skeleton of fore limbs of A Shark, B Polypterus, Amia (a Ganoid), D Cod. 

 a, 6, c basalia (&' ossification in b), r radialia, st fin rays (not all drawn). — Chiefly after 

 Gegenbaur. 



usually less well developed, or partly absent; there is often an 

 ossification of some parts. In the Teleostei the original 

 skeletogenous supporting pieces are very small, the fin-border 

 preponderating; the basalia are absent; the radialia are short and 

 few in number : they occur only as a transverse row of four, or fewer, 

 short rods, attaching the fin to the shoulder girdle, they are partly 

 ossified, and have been incorrectly termed " car pals" ; a few short 

 cartilaginous pieces may also be present. The Dipnoi are very 

 different ; there is a median, long, jointed, cartilaginous bar, bearing, in 

 the genus Ceratodus, two series, in Protopterus, a single row only, of 

 cartilaginous, jointed rays. (In Lepidosiren, the radialia are entirely 

 wanting) . 



