138 THE EVOLUTION OF MAN. 



parent-form of the entire group, must have been very nearly 

 allied to the Reptiles in its whole organization, even though 

 it cannot be regarded as a true Reptile in the present 

 meaning of the term. Of all known Reptiles, certain Lizards 

 are most nearly allied to the Protamnion ; and in the 

 outward form of its body we may imagine the latter as 

 an intermediate form between the Salamander and the 

 Lizard. 156 



The Comparative Anatomy and Ontogeny of the Am- 

 iiionate group clearly explains its genealogy. The group 

 which directly descended from Protamnion gave rise to two 

 divergent branches. The first of these, which will in future 

 receive our whole attention, forms the Mammalian group. 

 The other branch, which assumed an entirely different course 

 of progressive development, and which is connected with 

 the mammalian branch only as the root, is the compre- 

 hensive group constituted by Reptiles and Birds. The two- 

 latter forms may be classed together as Monocondylia, or 

 Sauropsides. The common parent-form of these is an; 

 extinct lizard-like Reptile. From this, the Serpents, Croco- 

 diles, Tortoises, Dragons, etc. in short, all the various forms 

 of the Reptilian group developed in different directions. 

 The remarkable group formed by the Birds also developed 

 directly from an offshoot of the Reptilian group, as is now 

 definitely proved. Down to a late time the embryos of 

 Reptiles and of Birds are yet identical, and even later the} 7 " 

 are in some respects surprisingly similar. (See Plate VI. Fig. 

 T and (7.) In their entire organization the resemblance 

 between the two is so great that no anatomist now denies 

 that the Birds originated from Reptiles. The Mammalian 

 line is connected at its roots with the Reptilian line, but 



