66 
DR. W. KOWALEVSKY ON THE 
case with our recent Paridigitata. If the Hippopotamus and Pliacoclicerus, Tragulus and 
Antilope , seem wonderfully different, as being on the furthest points of the radiating 
lines, still they have every one of them strikingly similar typical characters inherited 
from the ancestral form which was the common progenitor of them all. 
The chief and most obvious characters of a Paridigitate foot are to be seen in the 
shape and connexions of its two middle fingers ; therefore I will commence with these, 
and state some general features common to all Paridigitata, living or fossil, without 
exception. 
While, in the Imparidigitata, the axis in relation to which the whole foot is shaped is 
given by the middle or third digit, the axial line passing through its centre, we have in 
a Paridigitate foot always two middle digits (the third and fourth), which form the 
centre in relation to which the foot is arranged, the axial line passing in the interval 
between these two digits. These, then, may be taken as the principal digits of the 
manus and pes ; they exhibit nearly always a certain mutual symmetry, and are inter- 
locked at their upper extremities by a peculiar arrangement which is common to all 
fossil and living Paridigitata, as far as we know them now. 
The mutual interlocking of the middle metacarpals is effected in this way. The 
fourth metacarpal has always, at its upper radial end, a process, or a smooth salient 
margin, uninterruptedly connected with its proximal articular surface : this process enters 
deeply into a corresponding excavation of the third metacarpal ; and this excavation 
is overarched by a special ulnar process of the third metacarpal, which is inclined 
outwards, and abuts against the unciform. This is to be seen on all the figures of 
the carpus (Plates XXXVII. and XXXVIII.), and better still in Be Blainville’s Plates. 
In consequence of this projection of the third metacarpal the fourth stands always a 
little lower than its neighbour, and is supported entirely by the unciform, while the 
third is supported by the os magnum and partly by the unciform (Plate XXXVII. 
figs. 1, 2, 3, 20 ; Plate XXXVIII. figs. 5, 6), upon which it glides by means of its oblique 
outer and upper process. 
The two middle metatarsals (the third and fourth) (Plate XXXVIII. figs. 1 & 3) 
show us something quite analogous ; the fourth gives off from its upper tibial side a pro- 
minent process (not uninterruptedly connected with the proximal surface as on the fourth 
metacarpal), which enters into a deep corresponding cavity in the outer side of the third 
metatarsal. The fourth metatarsal is supported by the cuboid, the third by the third 
cuneiform. 
Such is the general rule of the interlocking of the two middle metacarpals and meta- 
tarsals in all living and extinct Paridigitata : there is not a single exception to it ; and 
the old Eocene Pichobune , as well as the recent Hippopotamus, present us with the same 
relation. But it may be urged against me that such a relation is certainly not to be 
seen in the recent Ruminantia, whose middle digits have coalesced into one single cannon 
bone. However, I think that the rule is even applicable to them. Although in the 
recent geological period the Ungulata Paridigitata, generally, acquired an exceedingly 
