170 COPE. [Vot. III. 
In the hind leg similar phenomena are exhibited. I. The 
fibula has been almost entirely excluded from the tibio-tarsal 
articulation. II. In some forms (the equine line) the tibio- 
astragalar tongue-and-groove joint has become oblique outwards 
and forwards. III. The astragalus (of the first tarsal row) has 
extended its distal articular surface on the cuboid (of the second 
row), so as to exclude more and more the calcaneum. 
That these changes, so remarkably similar in all of the artic- 
ulations of the legs, have resulted from the torsion in question, 
is rendered highly probable by the fact that they have appeared 
in all lines of descent, except that of the Amblypoda, in direct 
ratio to the advance of digitigradism in the Ungulata, and the 
measure of the one is a measure of the other. 
The movement involved in the preceding discussion is that of 
plantation. In recovery, we meet with another element in the 
problem. In spite of the outward rotation of the bones of the 
first carpal and tarsal rows, the bones of the second row have 
not moved outwards on the metapodials. They have remained 
stationary as regards the axis of support, while the me¢apodtals 
have been evidently pressed outwards. This is seen in two 
points. First, the external bone of the second row, the uncl- 
form, is in all Diplarthra much extended inwards. It reaches 
contact with the middle bone of the first row (the lunar) before 
the internal bone of the first row, the scaphoid, has extended 
outwards beyond the trapezoides to the magnum. This is the 
permanent state of affairs in the Amblypoda (Fig. 9). Second, 
the metapodial bones abut with the external sides of their 
proximal extremities against inner distal facets of the second 
row of tarsals. This must have been brought about by an 
inward movement of the second row of tarsal bones, or by an 
outward movement of the metapodials to meet them. The 
direct effect of the arrest of outward torsion of the foot is to 
‘dislocate the tarso-metatarsal and carpo-metacarpal articulations, 
unless some antagonistic movement prevent it. 
A strain antagonistic to the external movement of the tarsal 
bones is introduced at the moment of recover of the foot. Dr. 
H. Allen shows in his exposition of the Muybridge photographs, 
that in approaching the recover, the weight supported by the 
foot is transferred to its inner border, a movement which nec- 
essarily throws the strain on the external sides of the heads of 
