92 THE SUPERIOR EXTREMITY 



joints and proximally, at the bases of the metacarpal bones, by 

 fibrous partitions. On each side it is limited opposite the 

 borders of the second and fifth metacarpal bones. Incisions 

 through the aponeurosis are made between the tendons distally 

 and run transversely, so that they may be kept open by 

 the traction of the extensor tendons, thus ensuring good 

 drainage. 



In infections of the middle palmar space, " through and 

 through " drainage is obtained through the fourth interosseous 

 space and the dorsal aponeurosis. 



Insertion of the Digital Extensor Tendons. The tendons 

 of the extensor digitorum communis form a strong expansion 

 on the dorsum of the knuckles and first phalanx, which fuses 

 with the dorsal surface of the capsule of the metacarpo-phalangeal 

 joint. Into this expansion are inserted the tendons of the 

 lumbricals and interossei. On the index and the little fingers 

 the expansion is strengthened by the tendons of the extensor 

 indicis and quinti digiti proprius, which blend with it. The 

 central portion of the expansion is inserted into the base of the 

 second phalanx, while the collateral portions pass to the terminal 

 phalanx. 



When pus collects under the dorsal expansion it cannot 

 spread on to the dorsum of the hand until it has infected the 

 metacarpo-phalangeal joint. 



Radial Artery. On leaving the forearm the radial artery 

 winds round the radial side of the wrist lying on the radial 

 collateral ligament. It crosses the dorsal surface of the navicular 

 and the os multangulum majus (trapezium), and then passes 

 forwards into the palm at the proximal end of the first inter- 

 osseous space to form the deep volar arch (Fig. 30). 



The radial artery appears in the palm between the transverse 

 and the oblique heads of the adductor pollicis, and forms the 

 deep volar arch by joining the deep branch of the ulnar artery. 

 The arch lies deep to the flexor tendons and their synovial sheaths, 

 and, if haemorrhage from it cannot be controlled by pressure, 

 etc., recourse is usually had to ligature of the ulnar and radial 

 arteries. In this case the circulation is gradually re-established 

 through the volar and dorsal interosseous arteries (p. 71). 



The deep arch, which lies one finger's-breadth proximal to 

 the superficial arch, sends branches proximally to join the volar 

 carpal arch, and distally to join the digital arteries. 



Incisions on the Fingers. Incisions on the palmar aspect 



