THE FOOT. 245 
and concave foot which these made necessary to the well-being 
of the animal, fills up with a more elastic substance, better 
adapting it to the conditions of its summer range. 
If Ido not quite agree with Captain Hardy that the frog of 
the foot of the Caribou disappears in the fall by absorption, still 
the fact which he first mentions, so far as I know, is none the 
less significant. My own observations incline me to think that 
the frog disappears by abrasion and detachment. By taking 
the foot of the’ Caribou with the full frog and soaking it 
in diluted alcohol, or even in a weak brine, we may observe that 
the frog is laminated or arranged in layers, and after a while it 
becomes almost as soft as muck, and may be all removed by the 
finger up to a hard horny crust, capable of resisting abrasion 
almost as effectually as the outside of the hoof, leaving the hoof 
a thin plate, senseless and elastic. My own conclusion is that 
this inner wall, which is less dense, and through which the blood- 
vessels pass during the summer, and nourish the frog during its 
growth and maturity, becomes more indurated towards fall, and 
finally gradually closes those blood-vessels, when for the want of 
nourishment the frog dies, and becomes a dead, inert substance, 
and then decay and destruction commence. This first occurs on 
the lower surface, where it is exposed to abrasion, and proceeds 
gradually till all is gone; in the spring, when this peculiarity of 
the foot is no longer required, this plate, which constitutes the 
wall on which the frog is built, becomes softer, and allows the 
blood-vessels which pass through it to resume their functions, 
when the growth of the new frog is commenced, and proceeds 
rapidly till the foot is again filled with the rather soft, tough, 
and elastic mass, which comparative anatomists call the frog. 
The truth, however, can only be revealed by the microscope, 
and I now feel a self-reproach for leaving this undetermined. 
Others, I trust, will assume the task, who can perform it better 
than I can. These peculiarities in the feet of the Woodland 
Caribou I find even amplified in the Barren-ground Caribou. 
The hind feet are larger and broader than the fore feet. The 
hoofs on the hind feet of the former in my collection are two 
inches and six lines long at the cleft, and three inches broad, and 
measure five inches around the sharp edge from the point to the 
heel. The accessory hoof is two inches long, and one inch and six 
lines broad. In the accessory hoof the frog is but partially gone, 
but the edge is very sharp, especially at the point. The hoof of 
the fore foot is also two inches and six lines long, but is only two 
