244 



DIPNOI 



The pelvic girdle, unossified and known only in living genera, 

 is remarkably amphibian. It consists of a median ischio-pubic 

 cartilage. There are paired lateral or prepubic processes, and 



a large median epipubic process 

 (Fig. 213). 



The fin -skeleton has already 

 been mentioned (p. 106). In 

 Ceratodus both the pectoral and 

 the pelvic fins are leaf -shaped, 

 covered with scales, and with 

 dermal rays set all round both 

 along the preaxial and the post- 

 axial edges. They are provided 

 with a tapering segmented median 

 skeletal axis (Fig. 213). The first 

 segment articulates proximally 

 with the girdle and distally with 

 the second segment by means of 

 a true joint. In G. sturi it was 

 ossified. From the second out- 

 wards some twenty segments bear 

 preaxial and postaxial radials, of 

 which the latter are the smallest 

 and most numerous. When at 

 rest the preaxial margin of the 

 pectoral fin is borne upwards ; the 

 reverse is the case with the pelvic- 

 fin. Lepidosiren and Protopterus 

 have much reduced filamentous 

 paired fins, with a slender jointed 

 cartilaginous axis. The former 

 has lost all trace of lateral radials ; 

 but small preaxial radials remain 

 in Protopterus (Fig. 205). 



Ventral view of the pelvic girdle and fins The fin-skeleton is entirely 



of Ceratodus Forsteri, Kr. The skeleton of p nr Hlao-inrm<j i n livino- Dinnni anrl 



the right fin is completely exposed, a, jointed Cartilaginous in living JJipnOl, ana 



axis ; d.r, , dermal rays ; l.p, lateral process ; scarcely any traces of it remain 



m.c, median process; p, pelvic cartilage; . i r o- 



pr. r, postaxial radials ; pt.r, preaxial radials; in any known foSSllS. binCC, 



s, scaly covering of axial region. (Partly i ,1 i 11 i i j 



after Davidoff, from Quart. Journ. Micr. Sci.) however, these have all lobate 



fins like those of Ceratodus, there 



can be hardly any doubt, judging from the scale -covered axial 

 region, the dermal rays, and what remains of the axis in some 

 fossils, that the endoskeleton in the extinct Dipnoi was of essen- 

 tially similar character. It may safely be assumed that the 

 early forms had typical rachiostichous and mesorachic paired 

 fins. 



FIG. 213. 



