REGIONS OF THE HAND. 



527 



deep : the former have been already noticed ; 

 the latter are the median and ulnar. The first 

 passes under the annular ligament with the 

 flexor tendons; it then divides into five branches, 

 behind the superficial palmar arch. The first, 

 or most external of these branches, supplies 

 the short muscles of the thumb ; the second 

 sends one or two deep branches down to the 

 interossei, to communicate with the deep palmar 

 branch of the ulnar nerve ; it then finishes on 

 the outer side of the thumb; the remaining 

 three branches soon bifurcate, and are distri- 

 buted to the ulnar side of the thumb, to both 

 sides of the index and middle, also to the radial 

 side of the ring finger ; giving likewise a branch 

 to each corresponding lumbrical muscle. 



The ulnar nerve passes over the annular liga- 

 ment to the internal and posterior side of its 

 artery ; while passing over the ligament, it sends 

 the cutaneous branch to the skin on the hypo- 

 thenar, and then it divides into three branches : 

 first, the deep palmar branch, which accom- 

 panies the communicating branch of the artery, 

 and behind the deep palmar arch unites with 

 the branch sent from the median to supply the 

 deep muscles ; the next branch supplies the 

 ulnar side of the little finger and its muscles ; 

 while the remaining branches supply the col- 

 lateral nerves not furnished by the median, to 

 the radial side of the little, and the ulnar side 

 of the ring fingers. All these collateral nerves 

 accompany the corresponding arteries along the 

 sides of the fingers, giving numerous branches 

 in their course that terminate in the skin ; and 

 on the last phalanx they divide into two branches, 

 a dorsal and palmar : the dorsal, or ungual 

 branch, is lost in the skin, under the nail ; and 

 the palmar is expanded in the pulp of the 

 fingers. It is remarkable that the nerves of the 

 opposite sides of the fingers never anastomose. 



The muscles and tendons with which the 

 hand is pre-eminently endowed, lastly present 

 themselves for our consideration. In the upper 

 part of this region, or in front of the wrist, 

 there are scarcely any muscular fibres, except- 

 ing a small portion of the origins of the thenar 

 and hypothenar muscles ; and sometimes the 

 lower border of the pronator quadratus reaches 

 as far, or a little below the imaginary line w r e 

 have marked out as the superior boundary of 

 this region. But we have no lack of tendons 

 in this part; for we here find an assemblage of 

 them more numerous, and more tightly packed, 

 than in any other part of the body ; they are 

 also invested by synovial sacs, and pass through 

 the carpal ring, which was described in speak- 

 ing of the annular ligament in which they are 

 closely bound down. There are, however, some 

 that do not pass through this ring, and they are 

 the following : Most externally is the tendon 

 of the supinator longus, which terminates by 

 being inserted into the radius at the upper 

 boundary of this region ; then the tendons of 

 the extensores ossis metacarpi, and primi inter- 

 nodii pollicis. running in the most external 

 groove in the radius, which is converted into a 

 sheath for them by a process of the posterior 

 annular ligament. The radial artery passes 



under these, separating them from the joint in 

 its passage to the back of the wrist. 



More internally we have the tendon of the 

 flexor carpi radiafis passing into the palm, be- 

 hind the external reflected portion of the annu- 

 lar ligament, in a canal destined for it in the 

 scaphoid and trapezium ; the next tendon is 

 that of the palmaris longus, which here begins 

 to expand on the anterior surface of the annular 

 ligament, to which it is also attached; and 

 lastly, we find the flexor carpi ulnaris tendon 

 implanting itself into the pisiform bone. This 

 tendon, and those of the short extensors of the 

 thumb, form the lateral boundaries of this 

 region, dividing it from the dorsal. 



All the other tendons from the front of the 

 fore-arm pass through the carpal ring; they 

 are nine in number : Four of the flexor subli- 

 mis ; four of the flexor profundus, these are 

 all bound up in a common synovial sheath, 

 along with the median nerve; the remaining 

 tendon, that of the flexor pollicis, is situated 

 more externally, and has a distinct synovial sac. 

 All these tendons, after emerging from under 

 the annular ligament, diverge towards the differ- 

 ent fingers to which they are destined. In the 

 palm they are placed beneath the aponeurosis, 

 and lie upon the palmar interossei and the 

 adductor pollicis. 



As the muscles of the palm have already 

 been described, (see HAND, MUSCLES OF,) we 

 shall not notice them further than merely to 

 observe, that the intrinsic muscles of the thumb 

 and little finger constitute the external and in- 

 ternal regions of the palm, which they almost 

 solely occupy ; while the middle region, or 

 hollow of the palm, is occupied not only by 

 the remaining intrinsic muscles, (the interossei 

 and lumbricales,) but also contains the tendons 

 just described, with their synovial sheaths, as 

 well as the principal vascular and nervous 

 trunks of the hand. Wounds are therefore more 

 dangerous in the middle of the palm than on 

 either the external or internal regions, which 

 are constituted principally of muscle, having 

 but a thin aponeurosis and no important vessels 

 or nerves. It is also worthy of remark, that 

 the short muscles of the thumb, especially the 

 abductor, flexor brevis, and adductor, though 

 they act but indirectly on the first metacarpal 

 bone, present a serious obstacle to its dislocation 

 forwards ; their action tending to throw its base 

 backwards, whilst, by their bulk and tension, 

 they repel its attempts to slip forwards. 



Having now examined all the soft parts on 

 the palmar region, as nearly as possible in the 

 order in which they would have been exposed 

 by the dissector, we proceed to the second 

 division of our subject, and shall consider the 

 various layers of the dorsal region in similar 

 order. 



II. The dorsal region of the hand is convex 

 and irregular; the veins are large and promi- 

 nent. When the hand is extended the extensor 

 tendons stand out in strong relief, converging 

 at the wrist; and when flexed the heads of the 

 metacarpal bones and phalanges protrude. The 

 other prominent external characters of this 



