104 MAMMALIAN DESCENT. [Lect. VIII. 



Prototheria — tlie Oriiitiiorliyncus, and his distant rela- 

 tive the Echidna — ha^ e 1 yet found clearer evidence of 

 relationship wdth the Bird and the Reptile tlian in this 

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

 tilian characters ; they are only similar, suggesting a 

 <'ommon root-stock for all the three classes. In the 

 })alate of the Guinea-Pig I miss the median vomer 

 (ploughshare-bone), the proper vomer of the human 

 anatomy; a hinder and a front pair of vomerine Ijones 

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

 j^terygoid Ijones — internal pterygoid plates of Man — 

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

 Lizards, and Birds, Init 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, hasi-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 

 <leveloped, and the pterygoid bones at a distance from 

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

 Ixnie of the Frog, is present as two side pieces, the 

 remnants of the guard; the Flying Gat has only the 

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

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

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

 especially the La (tertian condition of the front ribs, 

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



