THE UPPER LIMB 395 



into the outer side of the base of the first phalanx of the index 

 finger, and the expansion of the extensor tendon on the back 

 of that phalanx. The second is inserted into the outer side, and 

 the third into the inner side, of the base of the first phalanx of the 

 middle finger, and both into the expansion of the extensor tendon 

 on the back of that phalanx. The fourth is inserted into the inner 

 side of the base of the first phalanx of the ring-finger, and into the 

 expansion of the extensor tendon on the back of that phalanx. 



Nerve-supply. — All the interossei are supplied by the deep 

 division of the ulnar nerve. 



Action. — (i) The palmar interossei are adductors, the fingers 

 which they adduct being the index, ring, and little. (2) The 

 dorsal interossei are abductors, the fingers which they abduct being 

 the index, middle, and ring, the middle finger having two abductors, 

 inasmuch as it can be drawn to either side of the middle line which 

 passes through its centre. 



In speaking of adduction and abduction reference is made to an 

 imaginary line passing through the centre of the middle finger, 

 adduction being movement towards that line, and abduction from 

 it. There is another very important action of all seven interossei, 

 in the performance of which they are assisted by the lumbricales. 

 This action is as follows : (i) to flex the metacarpo-phalangeal 

 joints, in virtue of their insertion into the first phalanges of the 

 four inner fingers, and (2) to extend their interphalangeal joints, 

 in virtue of their insertion into the expansions of the extensor 

 tendons. This action is well illustrated in making the hair- or up- 

 stroke in writing. 



Between the two heads of the abductor indicis superiorly is an 

 interval for the passage of the radial vessels, and between the two 

 heads of each of the other dorsal interossei superiorly there is an 

 interval for the passage of a superior perforating artery from the 

 deep palmar arch. 



Lymphatic Vessels of the Upper Limb. 



The lymphatic vessels of the upper limb are arranged in two groups — super- 

 ficial and deep. The superficial lymphatics lie in the subcutaneous tissue, 

 and the deep lymphatics accompany the deep bloodvessels. 



Superficial Lymphatics. — (i) Digital. — There are very rich networks of 

 lymphatics in the fingers, especially over their palmar aspects. The efferent 

 lyinphatics from the digital networks form two digital vessels, on either side 

 which he on each side of each finger, in contact with the corresponding digital 

 artery. At the roots of the fingers these vessels pass to the dorsal aspect 

 of the hand, and, after having communicated with each other and formed a 

 dorsal net\vork, they pass to the back of the wrist. 



(2) Palmar. — ^There is a very rich network of lymphatics in the palm, 

 from which several vessels emerge and pass in various directions — out- 

 wards, inwards, downwards, and upwards. The external efferent vessels pass 

 upwards and outwards over the thenar eminence, and join the lymphatics 

 from the thumb. The internal efferent vessels pass inwards, and, having 

 turned round the inner border of the hand, they join the lymphatics from 

 the little finger. The inferior efferent l^'mphatics pass downwards to the clefts 

 between the fingers, where they turn backwards and join the digital efferent 

 lymphatics. The superior efferent vessels ascend to the front of the wrist. 



