The Value of Paleontology. 3 
of structure to the corresponding parts of the known. This is not 
uniformly true. The law of variation intervenes, which ‘states 
that it may occur, that while one part of an organization occupies 
a relation of intermediacy, the other parts do not exhibit exactly 
the same relation. It is by the unequal mingling of structural 
points that new lines of succession are marked out. Thus it is 
that the power of reconstruction from fragments is limited, but 
not sufficiently so as to justify the epithet ‘‘pretension,’’ which 
has been applied to the claim made. Besides, two other laws re- 
main, which are of great importance to the paleontologist. 
Illustrations of the preceding laws may first be given. Ifa 
fragment of an animal be found, which contains acertain type of 
teeth known as the true selenodont, it is certain, in accordance 
with the law of uniformity of type, that the first bone of the hind 
foot of that animal (the astragalus) possessed two pulley-grooved 
faces, one above and one below, and not one only, as in most an- 
imals; also,:that the lower pulley face was succeeded by two sub- 
equal toes, and that the lateral toes were either reduced in form 
or wanting. There is no mechanical relation between the struc- 
tures of the teeth and foot; their accordance is simply a fact of 
type of a selenodont artiodactyle.* Again; if we find a portion of 
a foot which presents a joint between the first and second rows of 
bones which form the sole, we are absolutely certain that the ani- 
mal had the two outer ear bones external to the skull, forming a 
part of the lower jaw and the connecting rod by which the latter 
is attached to the skull. This is a type law of the bird and rep- 
tile. Again, if I find a part of a foot of the structure just named, 
where the first row of bones of the sole is united into one mass, 
and closely embraces the leg bone without being continuously 
united, I know that I have an animal with teeth, with a very long 
hip bone and a very long series of united vertebrae (or sacrum) 
resting upon it—in other words, a dinosaurian. ; 
The law of uniformity in successional relation is well illustrated 
by the genus Loxolophodon. The first bone of the foot (astraga- 
lus) of this animal, exhibits characters intermediate between that- 
of the elephants (Proboscidia) and odd-toed hoofed mammals 
(example, tapir) ; the remainder of the skeleton does the same ; 
3 Represented by a Kuminant, 
