90 MATERIALS FOR A MEMOIR OX 



cuboidal articulation into a convexo-concave joint, in forms in 

 which the oblique impact is cuboido-astragaloid, would look as 

 though such impact favored torsion. 



The study of the rotation of the limb is conveniently under- 

 taken in the elephant, since the fur is here absent. A number 

 of the positions assumed by the limbs is illustrated in series 

 733, Figs. 1 to 12. (See the figures of the fore limb of the 

 elephant.) 



The width of the limb at the elbow is observed to be less in 

 backward strain than in the recover. 



In Figs. 1, 2, 3, and 4 the olecranon is in line with the posterior 

 border of the arm above the elbow. 



In Fig. 4 the foot is leaving by its inner border. In Fig. 5 

 the olecranon is more in view, since it is turned out, at the same 

 time the foot is now everted [i.e., rotation outward has taken place 

 as the limb passes from impact of backward strain to that of re- 

 cover). Extreme position of eversion (Fig. 8) is coincident 

 with the distance between the olecranon and the humerus, and 

 the greatest reduction of distance between humerus and anterior 

 border of the arm. The posterior border of the arm is here 

 beginning to leave the side of the trunk, and a white light is re- 

 flected from over the triceps muscle. 



During the forward movements of Figs. 9 to 12 the limb is 

 slowly passing back to the position where the olecranon is again 

 in line with the posterior border of the limb (i.e., strictly speaking, 

 in profile of the limb), and the foot is preparing for a second 

 period of impact against the ground. 



The lighter shade of the prominence at the back of the elbow 

 answers to the position of the olecranon ; the elongated mass of 

 light shade which extends parallel to the arm between the elbow 

 and the shoulder answers to the position of the outer border of the 

 humerus. It is evident by the pictures that the distance between 

 the light over the humerus and over the olecranon is variable. 

 But it is known that the actual distance is invariable, and there- 

 fore the apparent variance is due to the motion of the limb in 

 rotation at the shoulder, by which the region of the back of the 

 elbow is moved somewhat outward. At the same time the dis- 

 tance from the outer border of the humerus and the anterior 

 contour is lessened as rotation takes place. These facts being 



