40 
DR. W. KOWALEVSKY ON THE 
inner malleolus. The outer distal edge is truncated somewhat obliquely, and has a 
groove in the middle for a corresponding convex ridge on the inner surface of the 
fibula, which fits the tibia in the same way as in Pigs, and being produced distally 
together with the internal malleolus, firmly clasps the astragalus (figs. 7 & 7', Plate 
XXXVI.). The posterior surface of the upper half of the tibia is very flat, showing 
some oblique, rough bony ridges for muscular attachment. 
The upper or proximal articular surface for the femur presented more resemblances 
to Suinse than with Ruminantia, especially in the deep outer groove for the muscular 
tendon, though the patellar fossa on the fore part of the crista anterior is shallower 
than in Sus. 
In the broken upper and lower halves of the tibiee of Hi/ojjotamus I find no difference 
from Dijilojms, save that of size. 
Dimensions of the Tibia. 
Diplopus 
(fig. 7, 
Plate XXXVI.). 
Hyopotamus. 
Ilordwell. 
Puy. 
Hempstead. 
Length 
280 
240 
Transverse breadth, proximal extremity .... 
G8 
55 
Transverse breadth, distal end 
431 
311 
36 
The Fibula . — Before describing this bone in the Hyojwtamidce , we must call to mind the 
principal differences it shows in the two series of Paridigitata and Imparidigitata. The 
proximal end is wanting in all our specimens ; but this is not of any consequence, as all 
the chief characters are presented especially by the distal extremity. In all Impari- 
digitata which possess a complete fibula, this bone is applied to the outer side of the 
tibia, forming at the distal extremity the malleolus externus (Plate XXXVI. fig. 7) ; 
this distal extremity is truncated obliquely in such a way that the inner surface of it 
articulates only with the astragalus, forming its outer boundary ; the fibula can never 
touch the calcaneum*, as this bone has no special surface developed on its upper lateral 
part to receive the distal end of the fibula. On the contrary, in all Paridigitata the 
fibula being applied in the same way to the tibia, presents at its distal end two articular 
facets for the articulation with two tarsal bones. The inner surface of the fibula 
(Plate XXXVI. figs. 7 & 7', and Plate XXXV. fig. 3, nat. size) is pressed against the astra- 
galus ; but its inferior extremity does not thin out, as in Imparidigitata, but is truncated 
at right angles, and provided with a special articular facet for an articulation with the 
outer wall of the calcaneum. We shall see hereafter that this outer wall exists 
perhaps also in the Imparidigitata, but that it is thrust under the astragalus ; and this 
seems to be the cause why the fibula of the animals belonging to this series cannot 
articulate with the calcaneum. 
'* Macrauchenia seems to present the single exception to this rule. The calcaneum of Macrauchenia is not 
known. 
