194 



SPECIAL PHYSIOLOGY. 



but outwards and forwards. In this socket, the articular surface of 

 the head of the humerus, which forms only J of a spheroid, instead of 

 f , as in the case of the femur, moves freely in all directions on the 



Fig. 53. Fig. 54. 



Fig. 53. Dorsal or back Tiew of the bom-s of the left hand, showing the smallness of the carpus, the light- 

 ness and length of the phalanges, the distinct position and length of the thumb. 1 to 8, carpal bones, viz.: 



I, scaphoid ; 2, semilunar ; 3. cuneiform ; 4, trapezium ; 5, trapezoid ; 6, os magnum ; 7, unciform ; 8, pisi- 

 form ; 9, 9, the five metacarpal bones, that of the thumb standing out from the rest; 10, 10, flrst phalanges ; 



II, second ditto; 12, last or ungual phalanges; *, sesamoid bones of thumb. 



Fig. 54. The radius and ulna of the left forearm, seen in front, tied together by their ligaments, to show 

 the mechanism of the joints concerned in pronation and supination. 1, the ulna; 2, the radius; 3, the ole- 

 cranon process, below which is the great sigmoid notch for the reception of the trochlear surface on the 

 lower end of the humerus; 4, the orbicular ligament, which springs from the ulna, and embraces the bead 

 of the radius, without being attached to that bone ; 5, the oblique or check ligament ; 6, the interoeseous 

 membrane; 7, the broad lower end of the radius, with which the hand is chiefly connected ; 8, the inter, 

 articular fibro-cartilage which passes from the edge of the lower end of the radius, to the styloid process at 

 the lower end of the ulna, without being attached to the lower articular end of the latter bone. 



scapula; but the joint is protected by the tendons of many muscles, 

 and is, moreover, overhung by one process of the scapula, above, named 

 the acromion process, and by another, the coracoid process, in front. 

 The elbow-joint (page 157) presents, on its inner side, a trochlear or 

 pulley-like surface, on the lower end of the humerus, which is received 

 into a deep notch (the greater sigmoid), Fig. 54, found on the front of 

 the olecranon process, 3, at the upper end of the ulna ; the two bones 

 are thus so securely fitted, that the ulna moves upon the humerus, in 

 the direction of flexion and extension only. At the outer side of the 

 elbow-joint, the lower end of the humerus is provided with a rounded 

 eminence, continuous with the trochlear surface just mentioned, and 

 having the upper end of the radius, 2, which is slightly hollowed, fitted 

 to it. The inner side of the head of. the radius, also smooth and artic- 

 ular, and therefore covered with cartilage, is received into a small 



