ANIMAL LOCOMOTION. 47 



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 which developed under the stimulus of 

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

 of the Academy of Natural Sciences of Philadelphia. 



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

 slightly inverted. This disposition is opposed by the peroneous 

 longus muscle which everts the foot. Coincident with the inver- 

 sion the external crucial ligament becomes tense and the tendency 

 to torsion is checked. 



The degree of outward rotation may be found to relate to the 

 swing of the trunk. In the elephant and the camel the rotation 

 is decided. In the goat it is apparently absent. It is less marked 

 in the horse than in the cat. 



The Act of Turning Round. 



In the dog the act of turning is accomplished in the following 

 manner : 



The hind feet remaining fixed, the body moves in front. It is 

 thrown laterally on one fore limb, so that this member becomes 

 more and more oblique to the line of gravity. At a time when 

 a line drawn upward through the supporting foot will lie entirely 

 free from the trunk the opposed limb has been placed in the line 

 of gravity and a new support assured. In the raccoon (series 745, 

 Fig. 17) the outer border of the foot is used for turning. 



Other figures which exhibit the phenomenon of the act of turn- 

 ing are those of the dog, the horse, the tiger, and the lion. 



On the Effect of Positions of the Limbs on those of the Head, 



the Neck, and tJie Trunk. 

 When the forward movement of the fore limb is the most con- 

 spicuous feature of the figure the head is erect. When the posi- 

 tion of backward strain is the most conspicuous the head is 



