120 LUNG-FISHES 
(Fig. 122), this plan of structure is somewhat obscured by 
the rudimentary character of the radial and basal elements, 
R+D, although the fin stem presents a well-marked 
jointed character, B. The pelvic girdle, a solid plate of 
cartilage, is produced anteriorly into a narrow median out- 
growth, PG, and laterally into a pair of dorsal spurs, PG’. 
The shoulder girdle is composed on either side of a large 
ventral element, SG, which meets its fellow in the median 
ventral line, and of a short dorsal element, SG’, which 
connects it with the skull. | 
aspects, showing pair 
M. Dental plates of (dentary) mandible; P. of palatopterygoid; V. of vomer. 
In the head region (v. pp. 252, 254), the brain case is 
cartilaginous, with, however, a few true bone centres (e.g. 
epiotic) appearing; the roofs of the skull and mouth, — 
together with the mandible, are well sheathed by dermal 
bones, as HP, N, PP, DN, AG. Paired dental plates 
fringe the rim of the mandible (Fig. 122 A, J/), the 
vomerine region (V), and the anterior end of the palato- | 
pterygoids (P). 
Fossil Lung-fishes 
The structures of the recent Dipnoans can as yet be but 
imperfectly compared with those of fossil forms. Their 
ancestral conditions can only be determined when more 
