1887.] NATURAL SCIENCES OF PHILADELPHIA. 65 



same in all animals. The leg is always carried in a direct path, the 

 limit of the movement being determined solely by the length of the 

 limb. In a Avord the forward movement is the less constrained in 

 the fore limb while the backward movement is the least constrained 

 in the hind limb. The most variable movements are the backward 

 for the fore-limb and the forward for the hind-limb. 



The foot in all animals excepting the horse (and even in this single 

 toed form the movement of the foot is nearly all essentials the same) 

 is carried forward in semipronation. The foot strikes the ground on 

 the outer border. Pronation now begins and is completed by the 

 time the perpendicular line is reached. The foot leaves the ground 

 by the inner border (the toes being successively abducted) so that 

 the pressure of the body is borne from without inward across the 

 foot. The foot is always everted as it leaves the ground. In a 

 plantigrade animal, as the raccoon, the foot is carried during the last 

 part of recover nearly parallel to the plane of support. In the 

 rapid motion of ungulates the foot may actually touch the 

 ground nearly to the hock. In backward strain the hock or 

 heel is gradually raised and at the end of strain the animal is seen 

 touching the ground by the tip of the inner functionally active toe. 

 In the horse the foot leaves by the tij) of the hoof. It is likely that 

 the degree of impact of the outer border of the foot will be found to 

 correlate mth the degree of development of the calcaneo-sural joint* 

 since the weight must be carried along the outer border to the rest 

 of tlie limb. At the end of backward strain the limb from the knee 

 distally is in the same line. The moment flexion begins eversion is 

 established, and the limb becomes angulated outward at the ankle. 

 The main axis of the proximal facet of the astragalus is correlative 

 with the degree of this obliquity. It is most pronounced in the 

 horse, less so in the ox, and scarcely at all in the hog. 



It has been already seen that when the limb is in the position of 

 arrest and the momentum carries the body beyond the perpendicular 

 line it is thrown into " backward strain." The instant that the strain 

 begins the knee is seen to move outward and the hock to move inward. 

 The parts of the foot below the heel remain unchanged. The impact 

 of the structures of the limb are thus impaired in backward strain. 

 It is well known that in the pentadacyle forms the foot can be 

 readily rotated at the medio-tarsal joint and it is a reasonable 



*A name proposed for the joint existing between the fibular process of the 

 calcaneum and the fibula or the tibia. 



