ANIMAL. LOCOMOTION. 55- 



and Solenodou. So far as observed, all mammals flex the toes of 

 the fore leg not only quicker than the hind, but more completely. 

 The adduction of the toes after the removal of the weight of 

 the body does not appear to be the result of a mechanical neces- 

 sity, for it is subject to variation. It is less prompt in the fore 

 limb than in the hind. At times when the hind foot is raised it 

 tends to be abducted. An example of such retention is seen in 

 series 594, Fig. 5. 



" Slowing Up."" 



The descent of the limb must have an appreciable eifect on the 

 momentum of the body by presenting a surface of resistance to 

 the air. This occurs in the manner made familiar by the bird in 

 the act of depressing the tail-feathers to arrest flight. Great 

 breadth of limb is therefore an unfavorable condition for rapid 

 locomotion. The figures of a cat jumping, as seen in series 719, 

 Figs. 1, 14, and 15, serve to illustrate the action. 



Position of Feet in the Last Stage of Recover . 



The feet in forward motion are carried in the position of semi- 

 pronation during the first stage of the movement. This act is 

 the best adapted to rapid action, since it presents the smallest 

 surface of the limb to the resisting air. (See p. 49.) 



The Angulation of the Limb at the Ankle due to Direction of the 

 Trochlear Axis of the Astragalus. (See p. 50.) 



Among the more pronounced correlations which exist between 

 the contour of the limb and the deeper structures is the shape of 

 the ankle. This is seen in the horse, the ox, and the hog. If the 

 astragalus of each of these animals is examined, it will be found 

 that the deflection of a line drawn through the upper or pulley 

 surface forms an angle with the axis of the limb of varying 

 degrees in the horse and in the ox, but none in the hog. The 

 production of such a line in the limb whose leg- and foot-bones 

 are in the positions assumed in life will show that the produced 

 line of the surface in the horse intersects the metatarsus twenty 

 centimetres below the proximal end of the bone, in the ox at 

 eleven centimetres, and in the hog the axis is parallel with the 

 tarsus. 



