342 On the Evolution of the Vertebrata, [ April, 
ments as thoroughly articulated for the use of the anterior leg as 
the Permian Theromorpha. In all the orders there is loss of 
parts, excepting only in the Ornithosauria and the Lacertilia. In 
the former the adaptation is to flying. The latter retain nearly 
the Theromorph type. An especial side development is the 
modification of abdominal bones into two peculiar elements to 
be united with the scapular arch into a plastron, seen in the Tes- 
tudinata. In this part of the skeleton the orders are generally 
degenerate, the last one, the Ophidia, especially so. 
The pelvic arch has a more simple history. Again in the 
Theromorpha we have the nearest approach to the Mammalia. 
The only other order which displays similar’ characters is the 
Ornithosauria (Dimorphodon, according to Seeley). In the Din- 
osauria we have a side modification which is an adaptation to the 
erect or bipedal mode of progression, the inferior bones being 
thrown backwards so as to support the viscera in a more poste- 
rior position. This is an obvious necessity to a bipedal animal 
where the vertebral column is not perpendicular, as in birds. 
And it is from the Dinosauria that the birds are supposed to have 
arisen. The main line of the Reptilia, however, departs from 
both the mammalian and the avian type and loses in strength. 
In the latest orders, the Pythonomorpha and Ophidia, the pelvis 
is rudimental or absent. © 
As regards the limbs, the degeneracy is well marked. No 
reptilian order of later ages approaches so near to the Mamma- 
lia in these parts as do the Permian Theromorpha. This approxi- 
mation is seen in the internal epicondylar foramen and well devel- 
oped condyles of the humerus, and in the well differentiated 
seven bones of the tarsus. The epicondylar foramen is only 
retained in later reptiles in the Rhynchocephalian Hatteria 
(Dollo); and the condyles of the Dinosauria and all of the other 
orders, excepting the Ornithosauria and some Lacertilia, are 
greatly wanting in the strong characterization seen in the Thero- 
morpha. The posterior foot seems to have stamped out the 
greater part of the tarsus in the huge Dinosauria, and it is re- 
duced, though to a less degree, in all the other orders. In the 
paddled Sauropterygia, dwellers in the sea, the tarsus and carpus 
have lost all characterization, probably by a process of degen- 
eracy, as in the mammalian whales. This is to be inferred from 
the comparatively late period of their appearance in time. The 
