156 MUSCLE TISSUE 



by the anterior and posterior oblique lines to its neck 

 and elbow-joint capsule. 



Extensor Ossis Metacarpi Pollicis. Origin, upper 

 part of the outer division of the posterior surface of 

 the ulna below the supinator brevis, from the middle 

 third of the posterior surface of the radius and inter- 

 osseous membrane between. Its tendon passes over 

 those of the radial extensors, and is inserted into the 

 radial side of the base of the metacarpal bone of the 

 thumb, and commonly by a slip into the trapezium, 

 its tendon usually splitting. 



Extensor longus pollicis arises below the extensor 

 ossis on the middle third of the ulna and from the 

 interosseous membrane for about one inch; its tendon 

 passes over the radial extensors, and is inserted into 

 the posterior aspect of the base of the last phalanx of 

 the thumb. 



Extensor Indicis Proprius.- Origin, from the ulna 

 below the extensor longus pollicis, and slightly from 

 the interosseous membrane and fascia over the exten- 

 sor carpi ulnaris; unites with the common extensor 

 tendon for the index, and forms the usual insertion. 

 This and the extensor minimi digiti tendon are always 

 on the ulnar side of the respective common extensor 

 tendons. 



Extensor Brevis Pollicis. Origin, small part of the 

 interosseous membrane and radius below the middle, 

 next below the extensor ossis; insertion, upper end of 

 the first phalanx of the thumb on its posterior aspect. 



The Muscles and Fasciae of the Hands 



Fascia of the posterior aspect is a thin layer prolonged 

 from the posterior annular ligament and blending with 

 the extensor expansions over the fingers; deeper than 

 this the interossei are covered by thin aponeuroses. 



Fascia of the palm consists of a strong central 

 part and two lateral portions which cover the short 



