THE WRIST AND HAND 



1425 



inence; thus, the knuckle is formed by the head of the metacarpal, the interphalangeal prominence 

 by the head of the first phalanx, and the distal one by the head of the second. Thus, the joint 

 in each case lies below the prominence, the distal joint being 2 mm. (^r in.), the interphalangeal 

 4 mm. {z in.), and the metacarpo-phalangeal 8 mm. (^ in.) below its prominence. 



Skin and skin-folds. — The skin over the palm is thickened over the heads of 

 the metacarpal bones and hypothenar eminence, thinner over the thenar. It is 

 peculiar in its absence of sebaceous glands and hair-follicles; hence the absence of 

 boils and sebaceous cysts. It is intimately connected with the palmar fascia, 

 hence the chief difficulty in operations when this is contracted. Over the pulp 

 of the digits the skin is closely connected with the periosteum of each ungual 

 phalanx. The importance of this is alluded to under the heading of whitlow 

 {vide infra). 



Skin -folds : two or three of these are seen on the palmar surface of the wrist: two lower down, 

 and usually close together, and one less well marked, a little higher up upon the forearm. None 

 of these corresponds exactly to the wrist-joint (fig. 1142). The lowest 'precisely crosses the arch 

 of the OS magnum in the line of the third metacarpal bone' (Tillaux), and is not quite 1.8 cm. 

 (f in.) below the arch of the wrist-joint. It is about 1.2 cm. (| in) above the carpo-metacarpal 

 joint line, and indicates very fairly the upper border of the transverse carpal (anterior annular) 

 ligament. 



'Of the many creases in the skin of the palm, three require especial notice. The first starts 

 at the wrist, between the thenar and hypothenar eminences, and, marking off the former emi- 



FiG. 1142. — Relation of the Volar Arches to the Folds of the Palm. (Modified from 



Tillaux.) 



flw 



Superficial volar arch — 

 Deep volar arch -- 



Superficial volar 

 Radial artery 



-Inferior fold 

 -Middle fold 



-Superior fold 



-Ulnar artery 



nence from the palm, ends at the lateral border of the hand and at the base of the index-finger. 

 The second fold is slightly marked. It starts from the lateral border of the hand, where the 

 first fold ends. It runs obhquely medially across the palm, with a marked inclination toward 

 the wrist, and ends at the lateral limit of the hypothenar eminence. The third, lowest, and best 

 marked of the folds starts from the little elevation opposite the cleft between the index and 

 middle fingers, and runs nearly transversely to the ulnar border of the hand, crossing the hypo- 

 thenar eminence at the upper end of its lower fourth. The first fold is produced by the adduc- 

 tion of the thumb; the second, mainly by the bending simultaneously of the metacarpo-phalan- 

 geal joints of the first and second fingers; and the third by the flexion of the three medial fingers. 

 The second fold, as it crosses the third metacarpal bone, about corresponds to the lowest part 

 of the superficial volar arch. The third fold crosses the necks of the metacarpal bones, and 

 indicates pretty nearly the upper limits of the synovial sheaths for the flexor tendons of the 

 three lateral fingers. A Uttle way below this fold, the palmar aponeurosis breaks up into its 

 four sUps, and midway between the fold and the webs of the fingers lie the metacarpo-phalan- 

 geal joints. Of the transverse folds across the fronts of the fingers, corresponding to the meta- 

 carpo-phalangeal and interphalangeal joints, the highest is placed nearly 18 mm. (f in.) below 

 its corresponding joint. The middle folds are multiple for all the fingers, and are exactly 

 opposite to the first interphalangeal joints. The distal creases are single, and are placed a Uttle 

 above the corresponding joints. There are two single creases on the thumb corresponding 

 to the two joints, the higher crossing the metacarpo-phalangeal joint obliquely. The free edge 

 of the web of the fingers, measured from the palmar surface, is about 1.8 cm. (f in.) from the 

 metacarpo-phalangeal joints. (Treves.) 



The superficial volar arch, formed by the ulnar anastomosing with the super- 

 ficial volar, or radialis indicis, will be shown by a line descending to the radial side 



