406 



MANUAL OF ZOOLOGY 



indicated by their name Dipnoi ; not only do these animals 

 breathe by means of gills like ordinary fishes, but they have 

 a highly developed apparatus for the respiration of air — 

 a single lung in the case of Ceratodus, a pair of lungs 

 (united in front) in the other two genera. They have bony 

 scales and dermal fin-rays ; but the paired fins are con- 

 structed on a totally different type from those of any other 

 living fish. The fin, pectoral or pelvic as the case may be, 

 is leaf-like, or very long and narrow, and the skeleton (Fig. 

 245) consists of a central axis in the form of a slender, taper- 



"? lam 



h^f/f ////// 



Fig. 245. — Ceratodus Forsteri. Lateral view of the anterior portion of the skeleton. 

 A, anterior median membrane bone of the roof of the skull; B. posterior median 

 membrane bone, has, basal cartilage of the pectoral fin; br, branchial arches; 

 7'«^,_inter-operculum; lam, plate overhanging branchial region; mck, Meckel's 

 cartilage; occ. rb, occipital rib; op, operculum; pal, palato-quadrate; pet, pec- 

 toral arch; rbs, ribs; sub. orb, sub-orbital bones; so, squamosal; supra, sc, 

 supra-scapula. 



ing, jointed rod of cartilage, with a row of smaller jointed 

 rods of cartilage on either side of it. This form of fin-skele- 

 ton, which occurs in certain groups of fossil fishes, as well as 

 in Dipnoi, has been termed the archipterygium. The noto- 

 chord is persistent, and the cranium (Fig. 245) consists of a 

 mass of cartilage with little ossification, but with the addition 



