A treatise on zoology . Fig. -277. Ventral view of the endoskeleton of the pelvic girdleanA &n of Polyodon folium, hac. (After Rautenfeld.) Pm,median, and Pit, dorsal ])rocess of girdle ; F, Fj, and Fo,nerve-foramina; 1-13, radials. ^ ACTINOPTER YGII 303 normal skeleton, conforming to the. The pectoral fin has a fairly rhipidostychous plan, with a postaxial axis (Fig. 27t)) ; but the pelvic fin has a remarkable structure, differ-ing from that of all other Osteichthyes. No definite line of demarcation exists between the pelvic gii-dle and the skeleton of the fin itself (Figs. 276-8). The radial
A treatise on zoology . Fig. -277. Ventral view of the endoskeleton of the pelvic girdleanA &n of Polyodon folium, hac. (After Rautenfeld.) Pm,median, and Pit, dorsal ])rocess of girdle ; F, Fj, and Fo,nerve-foramina; 1-13, radials. ^ ACTINOPTER YGII 303 normal skeleton, conforming to the. The pectoral fin has a fairly rhipidostychous plan, with a postaxial axis (Fig. 27t)) ; but the pelvic fin has a remarkable structure, differ-ing from that of all other Osteichthyes. No definite line of demarcation exists between the pelvic gii-dle and the skeleton of the fin itself (Figs. 276-8). The radials, forming a single series, are articulated to basals, whicli are more or less independent posteriorly, but become fused to the girdle in front. A skeleton is thus formed somewhat resembling that of Clado- selache, and suggesting a derivation from a primitive orthostichous type (Wieders- heim [492], Regan [345]) rather than from an out-standing axis in a projecting lobe (see p. 108). Dorsal processes, analogous if not homologous with the iliac process, aredeveloped along the basalregion of the fin of Polyo-don. In Scaphirhy7ichi(scataphradus the internalend of the pelvic cartilagemay be segmented off as aseparate element. So faras is known, the radialsof the dorsal and anal finsund
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