194 MAMMALIAN DESCENT. [Lect. VIII. 



Prototlieria — the Ornithorliyncus, and his distant rela- 

 tive the Echidna — have I yet found clearer evidence of 

 relationshijD with the Bird and the Reptile than in this 

 Rodent. Of course, these are not avian nor even rep- 

 tilian characters ; they are only similar, suggesting a 

 common root-stock for all the three classes. In the 

 palate of the Guinea-Pig I miss the median vomer 

 (ploughshare-bone), the j^i'oper vomer of the human 

 anatomy; a hinder and a front pair of vomerine bones 

 exist in this type. In the Mammalia, generally, the 

 pter3^goid bones — internal jDterygoid plates of Man — 

 are not free from the base of the skull, as in Snakes, 

 Lizards, and Birds, but they cleave closely to it, as in 

 Turtles and Crocodiles. Then, in the Mammalia and 

 the two last-mentioned groups, the skull does not give 

 off outstanding spurs, basi-pterygoids, as in those types 

 which have the pterygoids loose or free. But the 

 Guinea-Pig's skull is like that of Lizard, or Bird, 

 in respect of the basi-pterygoid spurs being well 

 developed, and the pterygoid bones at a distance from 

 the skull. The parasphenoid, or basi-cranial dagger- 

 ])one of the Frog, is present as two side pieces, the 

 remnants of the guard; the Flying Cat has only the 

 blade, as I showed in my last Lecture. The small 

 ])ones of the ear are very large and clumsy in the 

 Guinea-Pig ; and many other things in him are archaic, 

 especially the Lacertian condition of the front ribs, 

 in new-born Guinea-Pigs, as I long ago showed. 



