APPENDICULAR SKELETON — FISHES 



235 



Holocephals (fig. 247, C, D) are simple, having but a basipterygium 

 which supports all of the few radials. 



In the males of most Elasmobranchs (including the Holocephals) 

 one or more radiaHa near the end of the basipterygium are modified 

 to form the skeleton of the mixipterygium or 'clasper,' an organ used 

 in copulation. The form and number of parts of the mixipterygia 

 differ in different genera (fig. 248). 



In both pairs of fins the radials usually occur only on the preaxial 

 side of the basal cartilages, but in a few genera there are some radials 



Fig. 248. — Skeletons of pelvic fins of (,4) Raia (Goodrich, '09) and (5) Heterodontus 

 (Daniel, '15) showing claspers (mixipterygia). b, basipterygia; /, obturator foramen; 

 il, iliac process; ip, ischiopubic region; p, prepubic process; pr, pt, pre- and postaxial 

 radials; 1—4, cartilages of clasper. 



on the postaxial side (fig. 247, C, D), giving the distal part of the fin 

 a distinct biserial arrangement, this playing a large part in the 

 'Archipterygial Theory' of the fin (p. 241). 



The pelvic fins of Holocephals (fig. 247, C, D) are simple, having but a single 

 basal (basipterygium) which supports all of the few radials. In the pectoral 

 fin all three basals are present, but the propterygium alone {RhinochimcBra) or 

 largely {Chimara) is the element articulating with the girdle. 



TELEOSTOMES.— The modifications of the appendicular skele- 

 ton in the higher fishes does not keep pace with the systematic po si- 



