i84 
ON THE ERGOT OF EQUIDAE 
full)' (ievelopcd on the fore limbs. For example, I lyracothcrium, found in 
the lower Eocene, had four fully developed toes on the fore feet and two 
functional lateral toes on the hind feet ; other Taraeotherinae in the I^ocene 
and Oligocaen had somew hat rudimented lateral toes further from the ground, 
so that the function was lost, and the present horse uses only one toe to 
walk with. 
This theory has been proved b)' man)' naturalists, so that, from the de- 
velopment of the horse, we see that the fore foot has alwav's borne a larger 
number of fully developed digits than the hind foot. 
If we observe this development of the digits of the horse, and the condi- 
tion of the digits of all present mammals, that the greater development is 
always found on the fore feet, also that the callosity is either found on the fore 
feet alone, or is larger on the fore than on the hind feet, we must conclude 
that these facts are connected. 
From ni)' own histological obser\^ations and from these three facts, I 
infer that the Callosity must be a rudimentary digit. 
For the theorists who affirm that the Callosity is a rudimentary pad, I 
must write that with the ox and deer which are now true digitigrades, the 
organ that corresponds to the pad is greatly rudimented and is sometimes 
scarcely to be seen, especially the pad which should belong to the after-claws. 
Only at the junction of the claw wall and the common skin can a slight 
trace be discerned, but sometimes not even that. 
That, among the present Equidae, whose remote ancestors — those at least 
earlierthant he Hipparion, as fossils indubitabl)' show — had already develop- 
ed from plantigrades to digitigrades — a large rudimentary pad should still be 
seen, is cjuite impossible ! 
In order to conij)are the after claw with the ergot I should like first 
to write something of the after claw. 
The after claw of Ungulata, which is found on the fetlock, — of what use 
is this to its possessor? It is clear that this organ, which is not so rudi- 
mented, that is, not so far from the ground, as in the ox and deer, is found 
