1893-94.] Professor Ewart on Digits in the Horse. 
185 
The Second and Fourth Digits in the Horse : their 
Development and Subsequent Degeneration. By 
J. C. Ewart, M.D., Kegius Profe.ssor of Natural 
History, University of Edinburgh. 
Preliminary. 
(Read March 5, 1894.) 
During the last fifty years not a few familiar and apparently 
quite uninteresting structures have all at once assumed unusual 
importance and arrested the attention of naturalists in all parts of 
the world. This is especially true of what used to he known as 
rudiments, of what we nowadays generally designate vestiges. 
Of all the known vestiges, the most familiar are perhaps the 
“splint ” bones of the horse. For long the interest in these splints 
was extremely limited, but since it was shown that they correspond 
to the functional second and fourth metacarpals and metatarsals 
of other vertebrates they have attracted the notice of both com- 
parative anatomists and palseozoologists, and are now invariably 
looked upon as affording strong evidence in support of the view 
that the horse has descended from polydactylous ancestors. 
Since, through the work of Gaudry, Marsh, Cope, and others, it 
became possible to construct a wonderfully complete pedigree for the 
horse family, and especially since Huxley, in his address on “ Fossil 
Horses,” gave a graphic account of the ancestors of recent horses, 
many have wished that, by way of making the relationship with 
Hipparion still more certain, “ rudiments ” of the phalanges of the 
second and fourth digits could be shown to persist at the ends of the 
“splints.” Gegenbaur once suggested that there might be latent 
“germs” of the lost digits, but apparently no one has hitherto 
discovered the “ germs ” or rudiments in the embryo or found the 
vestiges in the adult. This being the case, it may seem strange that 
I am now in a position to assert that it is all but impossible to study 
the development of the horse without observing the development 
and subsequent degeneration of the second and fourth fingers and 
toes, or to examine the adult skeleton without seeing their vestiges.. 
