THORACIC LIMBS 601 



proximal border is continuous with the rounded proximal surface of 

 the bone. The surface on the process exhibits a wide, shallow groove, 

 which is covered with cartilage on each side and converted by strong 

 ligaments into a canal for the tendon of the flexor carpi radialis muscle. 



There is no radial surface to the bone proper, as the proximal and 

 distal surfaces meet in a sharp line, but the process of the bone exhibits 

 a rounded radial aspect which faces dorsally as well as radially, and 

 bears a circular facet for the sesamoid bone in the tendon of the 

 extensor ossis metacarpi pollicis muscle. 



Nomenclature. The scapho-luuar is composed of two bones, 

 separated in man and many animals, named the scaphoid and the 

 lunar, hence the name is a compound of the two words. In the human 

 hand the scaphoid has the shape of a keeled boat (in Greek scaphe) 

 and the lunar is cresceutic. The scapho-lunar is also called the radiale 

 and the intermedium. 



Determination. If the rounded proximal surface be held upward 

 and the triangular dorsal surface toward the student, the process of the 

 bone will point to the side to which the bone belongs. 



Articulation. The scapho-lunar articulates with the radius above, 

 with the cuneiform on the inside, and with the unciform, the magnum, 

 the trapezoid, and the trapezium below. 



Ossification. The scapho-lunar develops from at least two centres 

 of ossification, and sometimes from three, the third representing the os 

 centrale found normally in the carpus of some other mammals. 



THE CUNEIFORM. 



General Description. The Cuneiform is the small bone on the 

 ulnar side of the proximal row (Fig. 461). It may be distinguished 

 from the other small bones of the carpus by its stout oblong form and 

 its very convex proximal surface. 



The cuneiform has five surfaces. When the pisiform, which lies 

 behind it, is in place, the proximal surface appears as a ridge which 

 is about twice as long transversely as it is wide in a dorso-palmar 

 direction ; it faces to the ulnar side as well as upward, and is convex 

 in both directions. It is covered with cartilage, and articulates with 

 a facet on the anterior surface of the styloid process of the ulna. 



The ulnar surface passes without abrupt lines into the dorsal sur- 

 face in front and into the proximal surface above. On the palmar side 



