MUSCLES OF THE FORE ARM. 429 



from the back part of the radius just below the insertion of the 

 supinator brevis. It terminates in a rounded tendon which 

 passes over the tendons of the radial extensors, and through a 

 groove on the styloid side of the lower end of the radius. The 

 tendon is there invested by a bursa. 



It is inserted, by its tendon, into the base of the metacarpal 

 bone of the thumb, and into the external side of the trapezium. 



It extends the metacarpal bone of the thumb.* 



8. The Extensor Minor Pollicis Mantis, 



Is at the ulnar side of the last muscle. It arises, tendinous, 

 from the back of the ulna below its middle, and fleshy from the 

 interosseous ligament. It adheres to the radius, and terminates 

 in a tendon which passes through the groove in the styloid side 

 of the radius, along with the last named muscle. 



It is inserted into the first phalanx of the thumb, by its ten- 

 don, which is extended to the root of the second phalanx. 



It extends the first phalanx/f 



9. The Extensor Major Pollicis Manus, 



Arises, by a small tendinous, and an extensive fleshy origin, 

 from the back of the ulna above its middle, and from the inte- 

 rosseous ligament, also from the back of the radius; it terminates 

 near the wrist, in a tendon which passes through the groove on 

 the back of the radius near the ulna. The belly of this muscle 

 conceals, very much, the other extensors of the thumb. 



It is inserted, by its tendon, into the oblong transverse tu- 

 bercle, on the back of the base of the second phalanx of the 

 thumb. Its tendon is furnished with one synovial sheath, at the 

 inferior extremity of the radius, which extends to the carpus, and 

 another which is smaller, and is placed upon the carpus and 

 upon the base of the first metacarpal bone. 



It extends the second phalanx.J 



* Varieties. This muscle is sometimes double, and has several other modifi- 

 cations which it is unnecessary to state. 



f Varieties. This muscle is sometimes only an appendage of the preceding. 

 Occasionally, its tendon is confounded with that of the succeeding muscle. 



t Varieties. Sometimes this muscle is completely double. 



