58 
POPULAR SCIENCE REVIEW. 
in certain genera, after the manner of birds, than that what is 
among existing animals a class- characteristic, should disappear, 
especially as Morosaurus is one of those genera in which some 
of the vital organs made a remarkable approximation to the 
bird-type. Morosaurus had two rows of tarsal bones. The 
metatarsals are three, as in Laosaurus, four, as in Scelido- 
saurus, or five in number, as in Morosaurus ; but they are 
never anchylosed into one mass, as in Birds. The number of 
phalanges increases in the outer digits as in Birds and Reptiles. 
The claw phalanges are sometimes compressed from side to 
side as in Birds, sometimes from above downward, as in 
Reptiles. 
This survey of the osteology of the Dinosauria leads us, I 
think, to conclude that whatever the group eventually became, 
it originated in a close family relationship with the Crocodilia ; 
and that plan, which was never entirely obliterated, underwent 
a development in most parts of the skeleton, more perfect than 
is known to have occurred in any other group of animals. But 
this series of changes in the skeleton did not convert the 
crocodile into a bird or a mammal, or make it anything but a 
near ally of the crocodiles, which, owing to the influence of 
conditions of existence, came to simulate birds in some parts of 
the skeleton and mammals in other parts. But it is impossible 
to believe that these modifications of the hard parts of the 
animal went on without the soft vital organs changing also ; 
and all analogy would suggest that the change was progressive, 
so that the vital organs of the Crocodile may have greatly 
altered. But whether the progress extended so far that certain 
Dinosaurs became eventually changed into birds in all essen- 
tials of organization and in some parts of the skeleton, while 
others approximated to mammals, is a speculative problem, 
attractive in its plausible simplicity, with which facts do not 
yet enable us to deal in a satisfactory way ; though it must be 
admitted, they give some support to such an hypothesis. 
A satisfactory classification of the Dinosauria can hardly be 
made until we know far more of the fossil representatives of 
the group, more of the extinct reptiles of South Africa, of the 
Labyrinthodontia, of the Ichthyosauria, and of the Ornitho- 
sauria, for with all these animals Dinosaurs show some evi- 
dences of affinity. The higher Labyrinthodonts, which, in 
some unexplained reverence for formulas, have got themselves 
included in the Amphibia notwithstanding the characters of 
their skull and axial skeleton, certainly closely approach Croco- 
diles, and therefore Dinosaurs and Ichthyosaurs. The Ich- 
thyosaurs are perhaps such a group as the Dinosaurs might 
have become under aquatic conditions of existence ; for 
although the resemblances of Ichthyosaurs to ordinary Dino- 
