66 PROCEEDINGS OF THE ACADEMY OF [1887. 



assumption that it is at this joint that the distal part of the limb 

 moves when the entire limb rotates outward. The femur, the ])ones 

 of the leg, and the astragalus act as one factor ; and the calcaneum and 

 the remaining bones of the foot as the other factor. The socket for the 

 proximal motion occurs at the hip, and that for the distal at the 

 concavity of the scaphoid bone. There is also considerable motion 

 between the calcaneum and the cuboid bone and between the cal- 

 caneum and the lower end of the fibula, if this bone is present, or 

 with the outer end of the tibia if it is absent. Outward rotation of 

 the main portion of the limb carries the calcaneum slightly inward 

 by reason of the articulation between the calcaneum and the bones 

 of the leg, Facets are here present in most terrestrial mammals. 

 In the wombat the articulation is evident. It is present in a 

 rudimentary form in man. 



The outer surface of the calcaneum of the bear is marked by a 

 stout roughened ridge as it enters into articulation with the fibula. 

 In the dog the surface is a small embossment which probably is in 

 contact with the fibula only at the time of the backward strain. In 

 a single old dog examined the same ridge is present as in the bear. 

 A similar ridge Avhich develojDed under the stimulus of diseased 

 action is seen in the skeleton of the tiger in the Museum of the 

 Academy. 



As the knee is rotated outward the outer border of the foot is 

 slightly inverted. This disposition is Oi^j^osed by the peroneus 

 longus muscle Avhieh everts the foot. Coincident with the inversion 

 the external crucial ligament becomes tense and the tendency to 

 torsion is checked. 



The first movement noticed in the limb after it is beyond the 

 centre of gravity is the flexion of the foot. In the horse the hoof is 

 thrown backward and the under surface of the foot is directed back- 

 ward, the heel being raised first. The sole is next directed 

 upward. In animals possessing more than one functionally active 

 toe the toes are quickly adducted in the air so as to offer the least 

 resistance to the impetus of the entire body. Associated with the 

 above a pronounced flexion of all parts of the limb occurs excepting 

 at the hip, where the movement is slight. A movement of the thigh 

 toward the trunk is indeed discernible. In animals possessing long 

 thigh-bones, such as the elephant, the movement is more decided than 

 in the ungulates. The same remarks are applicable to the move- 

 ments of the humerus. The degree to Avhich flexion is carried is 

 more marked in the young than in the adult, and in terrestrial than 



