236 FOOT OF UNGULATES CHAP. 
the limb passes through the third finger, which is larger than any of 
the others, and is symmetrical in itself. In this the present group 
contrasts with the Artiodactyla, where the axis is not “ mesaxonic,” 
but where there are two digits, on either side of the axis, which are 
symmetrical with each other. This at rangement of the limbs is 
highly characteristic, but appears to be not quite universal. In 
the Titanotheres, which form a group of the Perissodactyles, the 
fore-limbs are not quite accurately mesax- 
onic. Nor on the other hand can all Ungu- 
lates which show the Perissodactyle condition 
be safely included in the present group. The 
ancient Condylarthra and the Litopterna 
show precisely the same state of affairs. 
But other features in their organisation lead 
to their separation from the Perissodactyles, 
of which, however, the Condylarthra are 
probably ancestors. The Litopterna on the 
other hand, which possess even one-toed 
members like Hqwus, are believed to repre- 
sent a case of parallelism in development. 
The number of functional toes varies from 
four to one. In the ankle joint the astra- 
galus either does not, or does only to a 
comparatively slight extent, articulate with 
the cuboid as well as with the navicular 
Fic. 122.—Bones of the bone. Moreover the fibula when present 
manus of Camel (Camelus : é 
Facirianies). an ‘* does not as a rule articulate with the 
Cuneiform i, Se m, caleaneum. In the opposed group of 
magnum j; R, radius ; 5, . . 
seaphoid ; td, trapezoid : Artiodactyles the precise reverse of these 
u, unciform. (From gonditions obtains. It is usually stated 
Flower’s Osteology. ) sein , : 
as part of the definition of this group 
that they do not possess horns of the type of those met 
with in the Cervicornia and Cavicornia. But the strong bony 
bosses on the skull of many Titanotheres, so curiously remin- 
iscent of those of the not nearly related Dinoceras and Proto- 
ceras, may well have supported horns of the Ox and Antelope 
pattern. 
The teeth of the Perissodactyles are lophodont, more rarely 
bunodont. The selenodont Artiodactyle form of molar is not 
met with. The dental formula, moreover, is at least near the 
