120 



LUNG-FISHES 



(Fig. 122), this plan of structure is somewhat obscured by 

 the rudimentary character of the radial and basal elements, 

 R 4- 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. 



Fig. 122 A. Jaws and skull of Protopterus annectans, figured in front and side 

 aspects, showing paired dental plates, x i. (After NEWBERRY.) 



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 FP, N, PP, DN, AG. Paired dental plates 

 fringe the rim of the mandible (Fig. 122 A, M), 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 



