r>46 



COMPARATIVE ANATOMY 



Protopterus and Lepidosiren. 



The skeleton of these lung-fish is largely cartilaginous but there is 

 a tendency toward ossification. The swim-bladder serves as lungs. The 

 very young individuals have long, feather-like external gills. 

 Appendix to the True Fishes. 



I. Palaeospondylidae (1 family between cyclostomes and fishes). 



II. Ostracodermi (3 orders of 8 families, mostly armored fishes). 



III. Antiarchi (1 family of mailed fishes). 



IV. Arthrodira (1 family of mailed fishes). 



e rntodiiit fimlr.ri (Australian lung-fsii) 



I.L 



Proloplerits anneclen* (African lung-fish) 



Fig. 372. Dipneusti. 



In C, snt., sensory tubes ; / /.. lateral line ; e.br., external gills ; pc.L, pectoral 

 fin ; op, operculum. In D and E, eg ., external gills ; PC., pectoral fin ; Pv., pelvic 

 fin. (A, after Giinther ; B, after Glaus ; C, after W. N. Parker ; D, after Budgett ; 

 E and F, after Graham Kerr.) 



It is well to note that 172 families of the 226 families of true fishes 

 are members of the order Teleostei. 



Of the Elasmobranchii there are 23 families now in existence and 

 9 extinct. 



The ganoids and dipnoi number 22 families. 



Amphibia. 



Contrasted with fishes, the amphibia have pentadactyl appendages, 

 while contrasted with reptiles, they possess double occipital condyles. 

 There are external gills in the larvae, though these do not always per- 

 sist. The adults breathe by lungs. The heart consists of two auricles, 

 one ventricle, a conus arteriosus, and a sinus venosus. 



Sub-Class I. Stegocephali. 



These are the extinct amphibia, many of which attained consid- 

 erable size. 



