PRACTICAL CONSIDERATIONS : SURFACE LANDMARKS. 621 



4. The oblique elevation beginning at the lower third of the forearm in the 

 interval left by the divergence of the supinator and the common extensor muscles, 

 and running downward and outward, to be lost on the posterior surface of the 

 thumb, represents the extensors of the thumb crossing over the tendons of the 

 extensores carpi radialis longior and brevior to their points of insertion (Fig. 582). 



5. The bony points to be seen and felt at the elbow and wrist 'have been de- 

 scribed in their practical relations in connection with the bones and joints (pages 

 287, 296, 308, 320, 330). The tendon most easily identified on the dorsum of the 

 wrist is that of the extensor longus poUicis when the thumb is strongly extended and 

 abducted. It is the posterior or inner boundary of the hollow at the base of the 

 thumb {vide infra), and its groove in the lower end of the radius is about the middle 

 of the posterior surface and just to the ulnar side of the prominent middle thecal 

 tubercle, — a useful landmark (page 296). The tendon, just before it reaches the 

 radius, corresponds approximately to the scapho-semilunar joint. 



The surface markings of the palm of the hand are often valuable landmarks. 



The most important are : ( i ) The triangle called the ' ' hollow of the hand, ' ' the 

 " cup of the palm," etc., the base of which corresponds to the three elevations oppo- 

 site the interdigital clefts, — formed by protrusion of fat between the flexor tendons 

 and the digital slips of the palmar fascia and by the distal extremities of the lumbri- 

 cales, — and seen best when the metacarpo-phalangeal joints are extended and the 

 interphalangeal joints are flexed. The sides of the triangle are formed by the thenar 

 and hypothenar eminences. Over this palmar hollow the intimate connection of the 

 skin and fascia is of practical importance (page 613). (2) The chief cutaneous 

 creases (Fig. 597) are four in number : (a) from just above the apex of the palmar 

 triangle to the radial side of the hand above the base of the index-finger ; {b') from 

 the lower end of a to a point a little above the middle of the ulnar border of the palm, 

 which it does not quite reach ; (r) from about the junction of the lower fourth 

 with the upper three-fourths of the ulnar border of the palm to a point a litde above 

 the cleft between the index and middle fingers ; (^) from b to r, often extending 

 upward towards the wrist and downward towards the base of the middle finger. 

 a and d are longitudinal, the former being caused by adduction of the first meta- 

 carpal, the latter by adduction of the fifth metacarpal bone, both movements being 

 towards the mid-line of the hand ; b and c are transverse, and are produced chiefly 

 by flexion (<^) of the first and second (r) of the three inner metacarpo-phalangeal 

 joints. 



a represents the inner border of the thenar eminence and therefore, approxi- 

 mately, of the outer group of the short muscles of the thumb and the inner margin of 

 the fascia intervening between them and the palmar space through which run the 

 flexor tendons. It intersects the deep palmar arch at about the highest point where 

 it crosses the metacarpal bone of the middle finger. 



b, at the centre of the palm, where it is intersected by </, crosses the same 

 metacarpal bone a line or two below, — i.e., nearer the fingers than the superficial 

 palmar arch, which runs about on a curved line from the lower border of the thumb, 

 when it is at right angles to the hand, to the pisiform bone. The deep palmar arch 

 is from a quarter to a half an inch nearer the wrist. 



c represents the upper limits of the synovial sheaths of the flexor tendons of 

 the index, middle, and ring fingers, is a little above the division of the palmar fascia 

 into the digital slips and the bifurcation of the digital arteries, crosses the necks of 

 the three inner metacarpal bones, and is as much above the corresponding meta- 

 carpo-phalangeal joints as they are above the webs of the fingers. 



d, at its upper portion, irregularly outlines the outer border of the hypoth- 

 enar eminence, — i.e., of the short muscles of the litde finger and of the fascia sepa- 

 rating them from the central space of the palm, — but it is the most irregular and 

 unimportant of these creases. The transverse folds on the palmar surfaces of the 

 fingers correspond, the highest to the web of the fingers, — i.e. , from one-half to three- 

 quarters of an Inch below the metacarpo-phalangeal joint, — the middle to the proxi- 

 mal interphalangeal joint, and the lowest to a line a little above the distal interpha- 

 langeal joint. On the thumb the line of the radial side of the index-finger, if 

 continued upward, almost coincides with the higher of the creases, which crosses the 



