1893 - 94 .] Professor Ewart on Digits in the Horse. 191 
In the specimen represented in figure V. the metacarpo-phalangeal 
joint and the capsule Avere Avell developed, and the tip of the digit 
(perhaps the relatively small third phalanx) was pointed and 
slightly movable. The epiphysis of the metatarsal (II.) was still 
cartilaginous. Figure YI. shows the distal end of the now fully- 
developed second metacarpal. The distal epiphysis, which is noAV 
very short, is ossified and fused to the shaft — only a faint streak 
indicating the line of junction. The free end of the epiphysis i& 
rounded and completely grasped by the now concave proximal end 
of the first phalanx. The cavity of the metacarpo-phalangeal joint 
had completely disappeared. I was not a little surprised to find in 
the one-month foal a separate terminal phalanx freely movable on 
the now greatly altered piece of cartilage representing the first and 
second phalanges. The fourth digit of the same manus was smaller 
and all the phalanges had completely blended. 
To complete the “ buttons,” all that is now necessary is that the 
united phalanges should undergo ossification, and afterwards fuse 
Avith their respective metacarpals and metatarsals. A fully developed 
“ button ” is represented on fig. VII. When the ossification sets in, 
hoAV many centres appear, and when the last trace of the presence of 
phalanges is obliterated, I have not yet been able to determine, but,, 
in all probability, early in the second year the “ buttons” completely 
coalesce Avith their “splints.” 
Having shoAA'ii that the second and fourth digits make their 
appearance during the development of the horse, another link has 
been added to the chain of evidence in favour of the horses of to- 
day being closely related to the three-toed horses of the Pikermi 
and other Miocene deposits, and remotely related to the primitive 
polydactylous horse-like forms of the Lower Eocene. It may, in fact, 
be said that the last link in the chain of evidence has at last been 
forged, and that there is noAv less than ever any escape from the 
conclusion that the horse has descended from polydactylous 
ancestors. Further, the presence of “rudiments” of the second 
and fourth fingers and toes in the embryo may help us in account- 
ing for the occasional presence of extra digits in fully-developed 
horses. 
