CLASS PISCES 



435 



fin-rays support the fins. Those of the first dorsal fin 

 (Fig. 372, Ri.), and at the anterior edge of the anal (^4) 

 and ventral fins (B), are unjointed and unbranched spines. The 

 caudal (S) and pectoral fins (Br) and most of the anal and ven- 

 tral fins are supplied with jointed, and usually branched, soft 

 Jin-rays. 



The endoskeleton (Fig. 372) consists principally of bones, and 

 includes the skull, vertebral column, ribs, pectoral girdle, and 



B 



Fig. 371. — Scales. A, ctenoid. B, ganoid. C, cycloid. (From the 

 Cambridge Natural History; A, B, after Gunther; C, after Parker and 

 Haswell.) 



the interspinal bones or pterygiophores (Fr) which aid in sup- 

 porting the unpaired fins. The body of the fish is to a consid- 

 erable extent supported by the surrounding water ; consequently, 

 the bones do not need to be so strong as those of land animals, 

 like birds and mammals, which must support the entire weight 

 of the body. 



The vertebra (Fig. 372, w) are simple and comparatively uni- 

 form in structure. They are called amphicoelous vertebrae 

 because the centrum has concave anterior and posterior faces. 

 A typical vertebra has a cylindrical supporting centrum, a neural 

 arch through which the spinal cord extends, a neural spine (oD) 

 for the attachment of muscles, and short ventral projections, the 

 par apophyses, to which the ribs are attached. The centrum 

 of one vertebra is connected with those of the preceding and 

 following vertebras by ligaments. The spaces between the centra 

 contain the remains of the notochord. 



