SKULL 



233 



developed in JVeoceratodus,^ and includes a small hyomandibular car- 

 tilage, a partially bony cerato-hyal and cartilaginous hypo-hyal and 

 basi-hyal element. In the other genera (Fig. 133) only a cerato- 

 hyal is retained. The branchial arches are but feebly developed 

 in the Dipnoi. Ncoccratodus has five, of which the first four are 

 divided into epi- branchial 

 and cerato -branchial seg- 

 ments, while the fifth is 

 undivided. Protopterus has 

 six, but only the second and 

 third are segmented as in 

 Neoceratodus.' In Lepido- 

 siren all the arches are 

 simple undivided rods. 



In all three genera the 

 skull conforms to the same 

 general type of structure, 

 but it is much more primi- 

 tive in Neoceratodus than 

 in the other two genera. 



With reference to the 

 fossil Dipnoi, it may be 

 stated that, so far as they 

 are known, the cranial 

 roofing bones are more 

 numerous than in the exist- 

 ing genera, and they cannot 

 readily be compared with 

 those of the latter, or with 

 the numerically reduced and 

 more definitely arranged 

 bones of most Teleostomi. 

 There is also evidence that in some fossil Dipnoi (e.g. Diptems) 

 the chondrocranium and the mandibular suspensorium (palato- 

 quadrate) must have been replaced by cartilage bones to an 

 extent which has no parallel in any of the surviving types.^ 

 Jugular bones were present in Dipterus and Fhaneropleuron. 



1 Ridewood, RZ.S. 1894, p. 6.32. ' Ibid. p. 638. 



3 Traquair, Ann. Mag. Nat. Hist. (5), ii. 1878, p. 1. 



Fig. 134. — Dorsal view of tlie skull of Lepido- 

 siren. a.n.c. Condyle on the quadrate cartilage 

 for the lower jaw ; n.sp, neural spine ; op, 

 operculum. For other reference letters see 

 Fig. 133. (From Bridge.) 



