180 MAMMALIAN DESCENT. [Lect. VII. 



ports the cartilaginous skull, but is distinct from it : 

 the blade underlies the orbital region; the guard the 

 temporal region — right and left ; and the haft the basi- 

 occipital. 



In air-breathing types, when the endo-cranium or 

 inner skuU becomes more and more solid, the cartilage 

 becoming transformed into bone, the parasphenoid 

 becomes inconstant. In Serpents there is only the 

 blade, in Lizards a rudiment, only, of that part ; in- 

 Crocodiles only a rudiment, right and left, of the guard ; 

 and in Chelonians (Turtles and Tortoises) none what- 

 ever. That it should be very large in all Birds, 

 although broken up into three centres of ossification, is 

 truly remarkable ; for the reptile is but a Pupa, in 

 respect of the Bird, which is an Imago, so to speak. He 

 who would find out this riddle must employ Darwinian 

 methods. The reptilian nature of Birds is doubted by 

 no one capable of judging ; but reptiles of the existing 

 type are not their progenitors ; and I question if any true 

 Amniotic (or true Eeptiles) ever were. Twenty years 

 ago I showed that the temporal scale squamosal of 

 the Ostrich family (flat-breasted Birds — Eatitise) was 

 a truly amphibian bone, just like that of a Frog or 

 Newt, and answering to both the " preopercular," and 

 " temporal scale," of a Ganoid Fish, in one single bon)^ 

 centre. That fact, the large size of the parasphenoid, 

 and other things that might be mentioned, being put 

 together, show conclusively, that the flying Fowl came 



