194 MAMMALIAN DESCENT. [Lscr. VIII. 



Prototheria the Ornithorhyncus, and his distant rela- 

 tive the Echidna have I yet found clearer evidence of 

 relationship 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 



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palate 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 bones 

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

 pterygoid bones internal pterygoid 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, 

 iin 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- 

 bone 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 

 bones 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, 





