THE FOEE-LIMB. 



43 



easily be inflated, either from the joint itself or through the opening). 

 The margin of the socket consists of a labrum, partly fibrous and 

 partly cartilaginous, which is easily removed entire. The capsule, 

 which is attached beneath the caput humen, arises from this. From 

 the articular cartilage of the ventral margin of the socket, and from 

 the adjacent part of the scapula, proceeds a strong band, which is 

 inserted into the flattened outer surface of the head. 

 2. The forearm. 

 The radio-ulnar, os antlhracJiu (Fig. 38). The two bony 

 elements of the forearm are fused into one, which, however, shows 

 traces of its compound character. Of these two bones, j-jg. 38. 



that which forms the inferior (in man anterior) border 

 is the radius, the other the ulna. The relative posi- 

 tions of the bony elements are such that they ap- 

 pear to be in a state of semi-pronation ; by this the 

 thumb-border of the arm is directed downwards (in 

 man forwards). The two bones so united form a 

 flattened, tube-like bone, the grooved surfaces of 

 which are directed inwards and outwards respectively; 

 the borders being dorsal and ventral. The shaft of 

 the bone is narrower above, becoming g-radually wider 

 below. In the upper half, the groove showing the 

 line of junction of the two bony elements is 

 scarcely visible, and it appears as though this part 

 consisted of ulna alone, the radius not reaching so 

 far; below the groove is more marked. The upper 

 articular extremity appears to consist of an olecranon 

 (Fig. 38 u') and a processus coi'onoidetis (/), between 

 which is the greater sigmoid cavity {cavitas sigmoidea viajor) for 

 the processus cubUalis humeri. A more careful examination shows 

 this to be incorrect : the portion of the concave articular surface, 

 which lies in the immediate neighbourhood of the ventral border, 

 undoubtedly represents the articular surface of the cap'dnlum radii, 

 and the upper portion of the articular surface (at n) belongs to the 

 idua and articulates with the trochlea (Figs. '^^, 36 t) of the 

 humerus. The inner border of the upper extremity of the bone 

 ai-ticulates with the groove t of the humerus. The inferior 

 extremity forms one of the usual cartilaginous epiphyses, enclosing 

 the two bones. That part of the extremity corresponding with 

 the radius is triangular and convex, it is prolonged upon the 

 inner or under surface of the bone by means of a process ; the 



Radio-ulnar of 

 the riglit side 

 of liana escu- 

 It'iif a, U\iciina.t. 

 size. 



r Radiiis. 



r' Capituhim ra- 

 dii. 



M Ulna. 



u' Olecranon. 



