528 



REGIONS OF THE HAND. 



region are, at the superior and external part, 

 when the thumb is extended and abducted, 

 au elongated depression, bounded externally 

 by the two short extensor tendons of the thumb, 

 and internally by its long extensor and the 

 tendon of the extensor carpi radialis longior. 

 In this depression the pulsation of the radial 

 artery may be felt, also the heads of the two 

 first metacarpal bones : internally and about 

 the same level there is a hollow corres- 

 ponding to the union of the wrist and hand ; 

 and at this point we can feel the tendon 

 of the extensor carpi ulnaris and the sty- 

 loid process of the ulna. When the thumb is 

 adducted the first dorsal interosseous projects 

 considerably. The fingers appear longer on 

 their dorsal aspect, the interdigital web that 

 was noticed on their palmar surface being here 

 wanting. 



1. The skin is very loose and thrown into 

 transverse folds ; opposite the two last joints of 

 the fingers may generally be seen three or more 

 transverse furrows; the middle one is the 

 deepest and most constant, and an incision 

 made about a line and a half below it will hit 

 upon the articulation. It resembles that on 

 the back of the fore-arm, but it gradually 

 thickens at the sides as it approaches the palmar 

 surface. Hairs and sebaceous follicles are 

 most abundant on the ulnar side of the back of 

 the hand and on the first phalanges. On the un- 

 gual phalanx, the skin, as it approaches the nail, 

 becomes tighter and glabrous, extends for about 

 two lines over the root of the nail, and is then 

 reflected back, so as to be continued over its 

 anterior surface to its free border, where it 

 becomes continuous with the skin of the pulp 

 of the fingers. It is in this portion of the skin 

 about the roots of the nails that the false whit- 

 low, called by the French tourniole, takes 

 place. It is an inflammation more of an 

 erysipelatous than a phlegmonous nature, some- 

 times attacking several fingers successively or 

 at once, therein differing from the true whitlow, 

 which is generally confined to one finger. 

 Warts also frequently occupy the skin of the 

 dorsum of the fingers, especially in those that 

 have to perform hard manual labour. 



2. The subcutaneous layer is very lax, serous 

 infiltration easily taking place; it contains no 

 pellets of fat like that of the palmar surface. 



The veins are subcutaneous, large and nu- 

 merous; all the large veins of the hand being 

 on its dorsal surface, the venous circulation is 

 not interrupted by the effort of prehension. 

 On the back of the fingers they form a com- 

 plete net-work, which gives rise to the dorsal 

 collateral veins of the fingers. At the inter- 

 osseous spaces these unite as the arteries di- 

 vide, and then proceed towards a kind of dorsal 

 venous arch, the concavity of which is upwards, 

 and from which arise larger branches; these, 

 in conjunction with one from the little finger 

 called the vena salvatella, and another from the 

 thumb called the cephalic, form the basilic and 

 cephalic veins described in the fore-arm. (See 

 FORE-ARM.) Some people prefer being bled 

 on the back of the hand, but, owing to the 



laxity of the skin and subcutaneous layer, con- 

 siderable extravasation of blood is apt to take 

 place. The subcutaneous nerves, derived from 

 the dorsal branch of the ulnar, and the ter- 

 minal branches of the musculo-spiral accom- 

 pany the veins, as also do the lymphatics. 



3. The apuneurosis is continued from that of 

 the back of the fore-arm ; it is strengthened 

 across the back of the wrist by strong parallel 

 oblique fibres, forming a band of nearly an 

 inch in breadth; which extends obliquely down- 

 wards over the extensor tendons from the sty- 

 loid process of the radius to the internal lateral 

 ligament of the wrist.* It sends down strong 

 processes between the tendons that convert the 

 grooves in the back of the radius and ulna into 

 sheaths, which are as follows: 1st, that noticed 

 on the palmar region for the short extensors of 

 the thumb ; 2d, for the radial extensors; 3d, for 

 the long extensor of the thumb; 4th, for the 

 extensor communis and indicator tendons; 

 5th, for the extensor minimi digiti ; 6th and 

 last, for the extensor carpi ulnaris. The meta- 

 carpal aponeurosis is very thin and split into 

 two layers ; the one separates the subcutaneous 

 layer, vessels, and neives from the tendons ; 

 the other covers the dorsal interossei, isolating 

 them from the tendons. 



4. The nerves are, externally, the radial, 

 which sends one branch, that, bifurcating, sup- 

 plies the thumb and radial side of the index 

 finger ; and another, which in like manner fur- 

 nishes the inside of the index and the middle 

 finger. Internally the posterior branch of the 

 ulnar supplies the two remaining fingers. These 

 branches receive frequent communicating ram uli 

 from the anterior collateral nerves. 



5. Tendons and muscles. The former are 

 less numerous on this region than on the pal- 

 mar ; the order in which they cross the wrist 

 was mentioned in describing the aponeurosis. 

 If the divisions of the extensor communis be 

 enumerated, they are twelve in number; four 

 of these are inserted at the base of the meta- 

 carpal bones of the thumb, index, middle, and 

 little fingers ; they are the extensor ossis meta- 

 carpi pollicis, extensores carpi radiales, and 

 extensor carpi ulnaris. The other tendons 

 proceed onwards to the phalanges. Those of 

 the common extensor are flattened and riband- 

 like; the three inner ones communicate with 

 each other, while that going to the index is 

 free. Opposite the metacarpo-phalangean arti- 

 culation these tendons narrow and thicken, 

 sending an expansion to either side of the 

 articulation: they again flatten on the first 

 phalanges, where they receive the tendons of 

 the lumbncales and interossei. At the articu- 

 lation of the first and second phalanges they 

 divide into three portions: a middle one, that 

 is inserted into the superior extremity of the 

 second phalanx ; and two lateral ones, that run 

 along its sides, reunite at its inferior end, and 

 are implanted into the upper part of the ungual 



* Generally called the posterior annular liga- 

 ment. 



