174 



SUB-CLASS GANOIDEI. 



there is an infraclavicle (clavicle, see note, p. 162). The skeleton 



of the pectoral fin is tribasal as in 

 Elasmobranchs ; it consists of three 

 basal somactids, carrying two rows 

 of peripheral somactids {r, r") to 

 which the dermotrichia are attached 

 (Fig. 101). The pro- and meta- 

 pterygium are ossified, the meso- 

 pterygium is mainly cartilaginous 

 but contains an ossification (o). 



The pelvic girdle is represented 

 by a small piece of cartilage (Fig. 

 102) to which the large ossified 

 basal somactid is attached. The 

 latter carries a row of ossified peri- 

 pheral somactids to which the der- 

 motrichia are attached. There are 

 no fulcra. There is a number of 

 dorsal fins in Polypterus, each 

 with an anterior spine ; and the 

 tail is diphycercal. 



In Polypterus there 

 are three main longi- 

 tudinal rows of valves 

 in the conus arteriosus with nine valves in each 

 row, and between these there are three incom- 

 plete rows of smaller valves (about forty-five in 

 all). Both ductus Cuvieri open into the 

 auricle. The spiracle is present, but the hyoid 

 gill and pseudobranch are absent. The ventral 

 aorta sends off a branch to the hyoid arch which 

 supplies the external gill of the larva. The 

 fourth branchial arch bears only one row of 

 filaments and has no slit behind it. The 

 stomach has a caecum and there is one pyloric 

 appendage. The air bladder is double and cel- 

 lular and its duct opens into the ventral wall of 

 the pharj^nx ; its blood supply is from the last 

 efferent branchial vessel and its vein joins 

 the hepatic. According to Budgett Polypterus is capable of 



Fia. 101.— Skeleton of pectoral fin 

 of Polypterus (from Gegenbaur). 

 R propterygium, R' metaptery- 

 gium ; ossification in meso- 

 pterygium ; r', r primary radials 

 (basal somactids) ; r" secondary 

 radials ; s fin rays. 



P 



Fig. 102. — 

 Pelvic girdle 

 p and skele- 

 ton of pelvic 

 fin of Poly- 

 pterus (from 

 Gegenbaur, 

 after v. 

 Davidoff). 6 

 basal somac- 

 tid ; r peri- 

 pheral somac- 

 tids ; p trace 

 of pelvic 

 girdle. 



