74 THE GENEALOGY OF THE VEKTEBEATA. 



of the most specialized of the Ungulates, the odd and 

 even-toed Diplarthra. 



The characters of the skeleton of the order Monotre- 

 mata shows that it is nearest of kin to the Reptilia, and 

 many subordinate characters point to the Theromorpha 

 as its ancestral source. 1 In the general characters the 

 Marsupialia naturally follow in a rising scale, as proven 

 by the increasing perfection of the reproductive system. 

 The Monodelx)hia follow with improvements in the repro- 

 ductive system and the brain, as indicated in the table 

 already given. The oldest monodelphia were, in respect 

 to the structure of the brain, much like the Marsupilia, 

 and some of the existing orders resemble them in some 

 parts of their brain-structure. Such are the Condylar- 

 thra and Amblypoda of extinct groups, and the Buno- 

 theria, Edentata, Rodentia and Chiroptera, recent and 

 extinct. The characters of the brains of Amblypoda 

 and some Creodonta are, in their superficial characters, 

 even inferior to existing marsupials. The divided uterus 

 of these recent forms also gives them the position next 

 to the Marsupialia. In the Carnivora, Hyracoidea and 

 Proboscidia a decided advance in both brain structure 

 and reproductive system is evident. The hemispheres 

 increase in size and they become convoluted. A uterus 

 is formed and the testes become external, etc. In the 

 Quadrumana the culmination in these parts of the struc- 

 ture is reached, excepting only that in the lack of separ- 

 ation of the genital and urinary efferent ducts, the males 

 are inferior to those of many of the Artiodactyla. This 

 history displays a rising scale for the Mammalia. 



Looking at the skeleton we observe the following suc- 

 cessional modifications : 2 



First, as to the feet, and (A) the digits. The Condy- 



1 Proceedings American Philosoph. Society, 1884, p. 43. 



2 See the evidence for evolution in the history of the extinct Mammalia. Proceeds. Amer. 

 Assoc. Adv. Science, 1883. 



58 



