OSTEOLOGY OF THE HYOPOTAMID2E. 
45 
and this to such an extent that even the seven bones of the carpus and tarsus, notwith- 
standing their irregular shape, were always arranged in the same way, so that a certain 
facet of one bone always touched a certain particular facet of another, and never other- 
wise. That this could really occur in every separate case of creation, is almost as pro- 
bable as that seven dice thrown out of a dice-box should give us the same number 
of points, similarly arranged in a hundred successive throws. Notwithstanding the 
thousands of different relations which might exist between such seven multangular bones, 
we get always only one ; and in the whole range of living and extinct animals we see no 
exception to the common rule of typical arrangement of the carpal and tarsal bones. 
The point at issue is, can this uniformity be accounted for by the principle of special 
creation, or by the theory of descent and modification'? No naturalist can in our time 
hesitate between the two ; and while all the adduced facts are wholly inexplicable by 
the first theory, they seem most natural in the light of the second. We may still not 
be fully informed as to all the true causes which induced the variation and consequent 
differentiation of animal types ; but the principle of descent must be conceded as the only 
one by which all future researches into the structure of the extinct world must be 
guided. 
I have mentioned chiefly the carpal bones ; but the study of the tarsus leads to pre- 
cisely the same result, and the likeness of the tarsal bones in all Paridigitata is perhaps 
even more striking than that of the carpals. All Paridigitata have a calcaneum with a 
special facet for the fibula, an astragalus with a double pulley, a cuboid supporting the 
fourth and fifth digits, and a navicular, with three cuneiforms, for the support of the 
third and second digits ; the first digit being always lost, its tarsal bone is gone to give 
support to the second toe, or, if this be lost, to the rudiment of it. We shall see these 
relations by-and-by, when we come to the special description of the tarsal and meta- 
tarsal bones. 
The Carpus of Hyopotamus, or the Four-toed Form. 
In describing the bones of the carpus of the Hyopotamus , I will try to confine my 
comparisons exclusively to the nearest living relatives of the extinct genus, as only 
such likeness and difference between nearly related forms belonging to one natural 
series can be of any immediate use for our purpose. Resemblances to the bones of 
animals belonging to other series are mostly only analogies, not homologies; and if 
some similarities which we may find to the carpal bones of animals belonging to the 
other natural series of Xmparidigitates are of importance as testifying their common 
descent from some ancient form, still we lack so completely any links between these two 
series (which are entirely distinct from the oldest Eocene deposits) that it would be idle 
to speculate about their relation on such trifling characters as these. I will therefore as 
much as possible confine myself to the series of Paridigitata. The carpus of Hyopotamus, 
like that of all Paridigitata, consisted of eight typical bones, four in each row; of these 
eight bones I have only five, the trapezium, pisiform and magnum being absent from 
n 2 
