

SURFACE ANATOMY OF THE UPPER EXTREMITY 1327 



epicondyle and nearer to this than to the lateral; when the forearm is fully flexed 

 the olecranon and the epicondyles form the angles of an equilateral triangle. On 

 the back of the olecranon is a smooth triangular subcutaneous surface, and running 

 down the back of the forearm from the apex of this triangle the prominent dorsal 

 border of the ulna can be felt in its whole length: it has a sinuous outline, and is 

 situated in the middle of the back of the limb above; but below, where it is rounded 

 off, it can be traced to the small subcutaneous surface of the styloid process on the 

 medial side of the wrist. The styloid process forms a prominent tubercle continuous 

 above with the dorsal border and ending below in a blunt apex at the level of the 

 wrist-joint; it is most evident when the hand is in a position midway between 

 supination and pronation. When the forearm is pronated another prominence, 

 the head of the ulna, appears behind and above the styloid process. 



Below the lateral epicondyle of the humerus a portion of the head of the radius 

 is palpable; its position is indicated on the surface by a little dimple, which is best 

 seen when the arm is extended. If the finger be placed in this dimple and the 

 semiflexed forearm be alternately pronated and supinated the head of the radius 

 will be felt distinctly, rotating in the radial notch. The upper half of the body of 

 the bone is obscured by muscles; the lower half, though not subcutaneous, can be 

 readily examined, and if traced downward is found to end in a lozenge-shaped con- 

 vex surface on the lateral side of the base of the styloid process; this is the only 

 subcutaneous part of the bone, and from its lower end the apex of the styloid process 

 bends medialward toward the wrist. About the middle of the dorsal surface of 

 the lower end of the radius is the dorsal radial tubercle, best perceived when the 

 wrist is slightly flexed; it forms the lateral boundary of the oblique groove for the 

 tendon of Extensor pollicis longus. 



On the front of the wrist are two subcutaneous eminences, one, on the radial 

 side, the larger and flatter, produced by the tuberosity of the navicular and the ridge 

 on the greater multangular ; the other, on the ulnar side, by the pisiform. The tuber- 

 osity of the navicular is distal and medial to the styloid process of the radius, and 

 is most clearly visible when the wrist-joint is extended; the ridge on the greater 

 multangular is about 1 cm. distal to it. The pisiform is about 1 cm. distal to the 

 lower end of the ulna and just distal to the level of the styloid process of the radius; 

 it is crossed by the uppermost crease which separates the front of the forearm from 

 the palm of the hand. The rest of the volar surface of the bony carpus is covered 

 by tendons and the transverse carpal ligament, and is entirely concealed, with 

 the exception of the hamulus of the hamate bone, which, however, is difficult to 

 define. On the dorsal surface of the carpus only the triangular bone can be clearly 

 made out. 



Distal to the carpus the dorsal surfaces of the metacarpal bones, covered by the 

 Extensor tendons, except the fifth, are visible only in very thin hands; the dorsal 

 surface of the fifth is, however, subcutaneous throughout almost its whole length. 

 Slightly lateral to the middle line of the hand is a prominence, frequently well- 

 marked, but occasionally indistinct, formed by the styloid process of the third 

 metacarpal bone; it is situated about 4 cm. distal to the dorsal radial tubercle. 

 The heads of the metacarpal bones can be plainly seen and felt, rounded in contour 

 and standing out in bold relief under the skin when the fist is clenched; the head 

 of the third is the most prominent. In the palm of the hand the metacarpal bones 

 are covered by muscles, tendons, and aponeuroses, so that only their heads can be 

 distinguished. The base of the metacarpal bone of the thumb, however, is promi- 

 nent dorsally, distal to the styloid process of the radius; the body of the bone is 

 easily palpable, ending at the head in a flattened prominence, in front of which 

 are the sesamoid bones. 



The enlarged ends of the phalanges can be easily felt. When the digits are 

 bent the proximal phalanges form prominences, which in the joints between the 



