322 



HOLOSTEI 



(Figs. 62-3). The lepidotrichia can be erected aud depressed in all 

 the fins except the caudal (Fig. 301 A). The median radials pro- 

 ject not at all beyond the level of the body-wall, and are composed 

 of three-jointed rods as a rule ; the proximal segment is long (inter- 

 spinous bone), the two distal segments short, the outer one being 

 rigidly fixed in the bifurcated base of the lepidotrich. The tail 

 is abbreviate heterocercal, homocercal, or of some more modified 

 type (p. 353) ; but the hinder end of the upper lobe of the hetero- 

 cercal tail of the larva (the axial lobe) is always lost during 



paisc 



FIG. 302. 



Skull of Salmo solar, L., cut longitudinally. (After Bruch.) a, angular; al, alisphenoid ; 

 ar, articular ; bo, basioccipital ; bsp, basisphenoicl ; d, dentary ; e.c, ethmoid cartilage ; no, 

 exoccipital ; h, hyomandibular ; li, ligament ; m.c, Meckel's cartilage ; mpl, metapterygoid ; 

 nipt, mesopterygoid ; mx, maxilla; osp, orbitosphenoid ; p, post-temporal; pa, palatine; pmsc, 

 premaxilla ; pro, prootic ; ps, paraspheroid ; pt, pterygoid ; q, quadrate ; so, stipraoccipital ; 

 sth, stylohyal ; sy, symplectic ; vo, vomer. 



development, and the notochord does not reach the extremity of 

 the tail in the adult. Therefore the adult caudal fin is formed 

 chiefly from the hypochordal lobe, but also to a small extent from 

 the epichordal lobe (Fig. 46). The radials of the paired fins are 

 still more reduced than in the Chondrostei. The clavicle is lost, 

 its place being taken by the cleithrum, and the endoskeletal pectoral 

 girdle is relatively small (Fig. 241). The maxilla generally both 

 acquires a free posterior end and bears one or two supra- 

 maxillary bones. In the two first sub-orders the lower jaw is still 

 provided with a dentary, angular, supra-angular (coronoid), splenial, 

 and articular (Figs. 237-240). Of the inferior gulars only a single 



