6oo 



HUMAN A^^ATOMY. 



Olecranon process 



^^^^r— Extensor carpi 

 '\^^J radialis longior 

 i^— ^ External condyle 



Anconeus 



Flexor carpi ulnaris 



Posterior 

 interosseous nerve 



Extensor ossis 

 metacarpi pollicis 



Extensor carpi ulnaris. 

 tendon 



Tendons of 

 extensor 

 communis 

 digit 



three obliquely transverse ten- 

 dinous bands (juncturae ten- 

 dinum), the one between the 

 index and median digits being, 

 however, frequently wanting. 

 As each tendon passes upon 

 the dorsum of the first phalanx 

 of its digit it spreads out into a 

 membranous expansion, which 

 receives the insertions of the 

 interosseous and lumbrical 

 muscles and then divides into 

 three more or less well-defined 

 slips. The median slip passes 

 to the base of the second pha- 

 lanx, while the lateral ones, 

 passing over the first interpha- 

 langeal joint, unite over the' 

 dorsum of the second phalanx 

 and are inserted into the base 

 of the third or distal phalanx. 

 Nerve-Supply. — By the 

 posterior interosseous branch 

 of the musculo-spiral nerve 

 from the sixth, seventh, and 

 eighth cervical nerves. 



• Action. — To extend the 

 phalanges of the second, third, 

 fourth, and fifth fingers and, 

 continuing its action, to extend 

 the hand. 



Variations. — The principal 

 variations of the common extensor 

 consist in the absence of one or 

 other of the tendons, usually that 

 to the fifth digit and more rarely 

 that to the second, or else in the 

 occurrence of additional tendons, 

 due to the division of one or more 

 of those typically occurring, cer- 

 tain of the digits then receiving 

 two or even three tendons. Oc- 

 casionally an additional tendon is 

 present which passes to the thumb 

 to unite with the tendon of its long 

 extensor. 



5- 



Dissection of posterior surface of forearm and hand, showing deep 



muscles. 



Extensor Minimi Dig- 

 iTi (Fig. 579). 



Attachments. — The ex- 

 tensor of the little finger (m. 

 extensor digiti quinti proprius) 

 arises in common with the 

 preceding muscle from the lat- 

 eral epicondyle of the humerus 

 and from the antibrachial fas- 

 cia. Its tendon passes beneath 

 the posterior annular ligament 

 in the fifth compartment and 

 fuses over the fifth metacarpal 



