1893-94.] Professor Ewart on Digits in the Horse. 
189 
especially the terminal phalanx. This is due to the fact that the 
vestigial fingers and toes are encased (wrapped up like mummies) in 
several layers of extremely dense connective tissue. In the 35 cm. 
embryo I only succeeded in completely unwrapping the second 
digit of the right manus, after prolonged maceration in cedar-wood 
oil.* When the investing structures were removed this digit had 
the appearance shown in figure II. The terminal phalanx was 
■curved inwards, and was almost an exact miniature of the corre- 
sponding phalanx in the manus of the polydactylous foal’s foot 
already referred to. Even more remarkable than the shape of the 
phalanx is the fact that its apex was encased in a small cellular cap 
(fig. II. a). This cap, which was easily detached, is difficult to 
account for. It may represent the bony cap which I recently found 
on the large middle digit of the horse, f or it may correspond to one 
or more of the deeper la37-ers of the hoof. 
The second digit of the manus is the one most frequently found 
in polydactylous horses. This being the case, it is worth noting 
that the phalanges of the second digit of the manus in normally 
developing horses appear to be always larger and better developed 
than those of the fourth, and also that the vestigial digits of the 
manus seem to be better developed than those of the pes. 
In no instance have I found the second and fourth digits better 
developed than in the 35 cm. embryo. In most of the older 
embryos examined marked degeneration had already set in. 
In some cases, up to within two months of birth, they, though 
much larger, closely resembled the digits in the 35 cm. embryo. 
In other cases the joint between the second and third phalanges 
early disappeared, with the result that each of the second and 
fourth fingers and toes were represented by single elongated 
pieces of cartilage connected by a fairly well-formed joint to the 
npiphysis at the end of their respective metacarpals and metatarsals. 
Hence it may be inferred that the second stage in the retrogressive 
process consists in the complete disappearance of all indication of a 
joint between the first and second phalanges and the all but complete 
disappearance of the joint between the second and third phalanges. 
I may mention that on removing the investing tissues I noticed what 
looked extremely like vestiges of the flexor tendons. 
t Ewart, Jour, of Anat. and Phys., January 1894. 
