ZO SOLID-HOOFED PIGS CHAP. 
of these, and that which has given its name to the group, 
concerns the arrangement of the digits. Instead of there being 
but one prevailing digit—the third, in the hand and _ foot, 
through which the axis of the foot passes, there are two, numbers 
three and four, between which the same axis passes, and which 
are perfectly symmetrical with each other. This type of foot has 
been termed “ paraxonic,” as opposed to the “ mesaxonic ” Perisso- 
dactyle foot (see Fig. 121 B, p. 235). It has been attempted 
to prove that the single prevailing digit of the Horse’s foot is a 
fused pair of digits, and the state of affairs which characterises 
the Camel, where the two metacarpals or metatarsals are to an 
almost complete extent united, has been urged in proof; so, 
too, certain abnormalities, such as those called “ solid-hoofed 
pigs.” These latter are simply Pigs in which the two central 
metacarpals and the terminal hoofs are completely fused with one 
another. In some of such cases there is not the slightest trace of 
the union of the separate metacarpals and phalanges. Even the 
sesamoid bones, attached behind to the toes, are two in number 
instead of four. And, furthermore, the tendon supplying the 
bones is single, though showing traces of its double origin. 
Such Pigs often show the abnormality from generation to genera- 
tion, and they proved convenient for those whose scruples would 
not allow them to eat the flesh of a beast “ dividing the hoot” 
and not chewing the cud. More singular still, as showing a 
pathological approach from another side to the Perissodactyle 
condition in an Artiodactyle, is a calf, where the foot ended in 
three equi-sized digits, of which the middle one lay in the longi- 
tudinal axis of the limb. From the opposite side cases are 
known of a Horse with a spht hoof and phalanges, thus present- 
ing the most striking likeness to a Camel. 
There is, furthermore, in certain groups of Artiodactyles 
(e.g. the Tragulidae) a tendency for the two middle metacarpals to 
unite, quite apart from such “sports” as those illustrated by the 
cases just set forth. And, as already mentioned, the union of the 
two middle metacarpals culminates in the Camel, Ox, ete. There 
is, however, absolutely no trace of such a fusion in the series of 
Perissodactyle animals known to us; and it would be by fusion 
rather than dismemberment that, as it would appear on this 
theory, the modern Ungulate foot has been arrived at. Of course 
' See Bateson, Materials for the Study of Variation, London, 1894, p. 387. 
