348 On the Evolution of the Vertebrata, [April, 
It will be readily seen from the above diagram that the discov- 
ery of the Condylarthra was an important event in the history of 
our knowledge of this subject. This suborder of the Lower 
Eocene epoch stands to the placental Mammalia in the same rela- 
tion as the Theromorphous order does to the reptilian orders. It 
generalizes the characteristics of them all, and is apparently the 
parent stock of all, excepting perhaps the Cetacea. The discov- 
ery of the extinct Bunotherian suborders united together insepa- 
rably the clawed orders, excepting the bats; while the .extinct 
order Amblypoda is the ancestor of the most specialized of the 
Ungulates, the odd and even-toed Diplartkra. 
The characters of the skeleton of the order Monotremata show 
that it is nearest of kin to the Reptilia, and many subordinate 
characters point to the Theromorpha as its ancestral source! In 
the general characters the Marsupialia naturally follow ina rising 
scale, as proven by the increasing perfection of the reproductive sys- 
tem. The Monodelphia follow with improvements in the reproduc- 
tive 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 Marsupialia, and some of the existing orders 
. tesemble them in some parts of their brain-structure. Such are 
the Condylarthra and Amblypoda of extinct groups, and the 
Bunotheria, 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 Car- 
nivora, Hyracoidea and Proboscidia a decided advance in both 
brain structure and reproductive system is evident. The hemi- 
spheres increase in size and they become convoluted. A uterus 
is formed and the testes become external, etc. In the Quadru- 
mana the culmination in these parts of the structure is reached, 
excepting only that in the lack of separation 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 ‘successional 
modifications :? 
1 Proceedings American Philosoph. Society, 1884, p. 43. 
* See the evidence for evolution in the history of the extinct Mammalia. Proceeds. 
Amer, Assoc, Adv. Science, 1883. 
