No. 2.] THE HARD PARTS OF THE MAMMALIA. 185 
of the radius downwards instead of upwards. This movement 
may be called antisupination. In it the palm is presented out- 
wards, and, when the humerus is flexed backwards, backwards 
also. This is its normal position when pushing the earth back- 
wards from its burrow, and the muscles to accomplish this move- 
ment are enormously developed. These include the subscapula- 
ris, infra. and supraspinosus, and the triceps extensor. The 
act of antisupination of the manus is performed by the pronator 
muscles of the fore arm, and the effect of the rotation inwards 
of the distal end of the radius is to throw the proximal end out- 
wards, so that it comes to be as external to the ulna at the coty- 
lus, as in a quadrumane. The external condyle of the humerus 
is thus especially developed to receive it. In the act of anti- 
supination the head of the radius describes a movement in the 
transverse direction towards the external epicondyle, and the 
external condyle has been extended in that direction as a conse- 
quence of the continued thrust. 
c. The Femoro-tibial Articulation. The existence of tibia and 
fibula of subequal size gave rise to two distal articular surfaces 
of the femur. The constant use of these in flexion and exten- 
sion gave them the convexity which they possess in the Mam- 
malia, a process already commenced in the Reptilia. The strong 
tendon of the rectus muscle passing over the anterior face of the 
extremity gave rise to the rotular groove. This became better 
defined and more important after the development in placental 
mammals of a sesamoid bone, or patella, in the tendon. The tor- 
sion of the femur on the arrest of the foot by the earth is, as 
with the humerus, from within forwards and outwards. To this 
cause, plus the impact, we may assign the production of the 
crest of the tibia in the same direction. The reason why, in the 
Reptilia, the fibula diminished in size, and the head of the tibia 
so expanded as to support the greater part of the external con- 
dyle of the femur, I am not at present able to suggest. 
ad. The hinge between the first and second series of tarsal bones 
in the Artiodactyla may be accounted for by reference to the 
habits which are supposed to have caused the cloven-footed 
character. Observation on an animal of this order walking in 
mud, shows that there is a great strain anteroposteriorly trans- 
verse to the long axis of the foot, which would readily cause a 
gradual loosening of an articulation like that connecting the two 
