94 THE SKELETON OE THE HOHSE 



(abbreviated) names and relative positions of tiie bones of the left carpus are in- 

 dicated below: 



Proximal Row: 

 Radial Intermediate Ulnar Accessory 





ri- 

 al 



?0 



Distal Row: 

 First Second Third Fourth 



The Radial Caiu'al Bone 



The radial carpal bone (Os carpi radiale)Us the largest bone of the proximal row; 

 it is somewhat compressed transversely, and is clearly six-sided. The proximal 

 surface is convex in front, concave behind, and articulates with the medial facet 

 on the distal end of the radius. The distal surface is also convex in front and con- 

 cave behind; it articulates with the second and third carpal bones. The lateral 

 surface bears upper and lower facets on its anterior part for articulation with the 

 intermediate; between and behind these it is excavated and rough. The dorsal 

 surface is rough and slightly convex. The medial surface and the volar surface 

 are rough and tuberculate. 



The Intermediate Carpal Bone 



The intermediate carpal bone (Os carpi intermedium)^ is somewhat wedge- 

 shaped, wider in front than behind. The proximal surface is saddle-shaped, and 

 articulates •\\'ith the middle facet on the distal end of the radius. The distal sur- 

 face is smaller, convex in front, concave behind, and articulates with the third and 

 fourth carpal bones. The medial surface has upper and lower facets for articula- 

 tion with the radial carpal, and between these it is excavated and rough. 

 The lateral surface is similar to the preceding and articulates with the ulnar car- 

 pal. The dorsal surface is rough and slightly convex. The volar surface bears a 

 tuberosity on its lower part. 



The Ulnar Carpal Bone 



The ulnar carpal bone (Os carpi ulnare)^ is the smallest and most irregular 

 bone of the proximal row. The proximal surface is concave and fits the lower part 

 of the lateral facet on the distal end of the radius. The distal surface is oblique 

 and undulating for articulation with the fourth carpal bone. The medial surface 

 has upper and lower facets for articulation with the intermediate. The dorsal and 

 lateral surfaces are continuous, convex, and rough. The volar surface is oblique, 

 and bears a concave facet for articulation with the accessory carpal bone; below 

 this is a tubercle. 



The Accessory Carpal Bone 



The accessory carpal bone (Os carpi accessorium)* is situated behind the ulnar 

 carpal bone and the lateral part of the distal end of the radius. It is discoid and pre- 

 sents for description two surfaces and a circumference. The medial surface is con- 

 cave and forms the lateral wall of the carpal groove. The lateral surface is con- 

 vex and rough; a smooth groove for a tendon crosses its anterior part obhquely 

 downward and slightly forward. The dorsal border bears two facets; the proximal 

 one is concave and articulates with the back of the lateral facet on the distal end of 

 the radius; the distal one is convex and articulates with the ulnar carpal bone. 

 The remainder of the circumference is rounded and rough. 



1 Also known as the scaphoid. 2 ^jg^ known as the semilunar or lunar. 



' Also known as the cuneiform. 



^ Also known as the pisiform and erroneously as the trapezium. 



