M. EXTENSOR (CARPI) RADIALIS BREVIOR. 269 



Dissection. Just dorsad of the insertion of the supinator longus is the oblique border 

 of the strong tendon of the M. extensor ossis metacarpi polliois. Entad of this tendon may 

 be seen another tendon evidently continuous with the muscle lying along the cephalic bor- 

 der of the antebrachium. With the tracer, separate the tendon- into two, an ectal and 

 more slender, and an ental and thicker. The former may be traced proximad for two 

 fifths of the length of the antebrachium, where it is continuous with its muscle, the extensor 

 carpi (radialis) longior. 



Divide the muscle at the middle ; in reflecting the proximal end, note that it becomes 

 thinner and wider, is wedged somewhat between two subjacent muscles, and, at the 

 humerus, has a third or a fourth overlapped by the muscle arising just distad of it. 



By pulling upon the tendon, and alternately flexing and extending the manus, it may 

 be seen that the tendon passes across the carpus entad of the oblique tendon of the exten- 

 sor metacarpi pollicis. With the arthrotome, cut the fascia at one side of the tendon upon 

 the carpus, introduce the tracer, and thus indicate where more incisions may be made so 

 as to expose the whole tendon as far as the proximal end of the indical metacarpal. 



Note that, in its passage over the distal end of the radius, the tendon lies in a groove 

 upon the dorso-cephalic side of the bone, separated by a triangular elevation from the 

 groove for the tendon of the extensor metacarpi pollicis. 



% 695. Remark. By analogy with the less modified leg, the muscles of the arm which 

 lie upon the dorsal aspect of the antebrachium and are inserted upon the carpus should be 

 called flexors, and those upon the caudal aspect extensors. These and other considerations 

 have been presented by the senior author (1 and 4). In an ideal myological nomen- 

 clature, we believe the muscles should be named as above, but in the present practical 

 work it seems best to retain the designations commonly accepted. 



Origin. By fleshy fibers from the epicondylar ridge of the humerus, between the 

 origin area of the supinator longus and a point opposite the distal end of the Foramen epi- 

 trochleare. The larger part of the origin line lies between the slender distal prolongation 

 of the origin area of the brachialis and the triangular origin area of the cephalic division of 

 the entotriceps. The distal fourth or fifth is just ventrad of the origin line of the extensor 

 communis (digitorum). 



Insertion. By a long tendon upon the dorsal border of the proximal end of the indi- 

 cal metacarpal. 



Remark. Like other tendons which pass over the wrist, this is held in place by liga- 

 mentous bands representing parts of the annular or armillary ligaments. 



M. EXTENSOR (CARPI) RADIALIS BREVIOR. 



696. Synonymy. The human muscle of the same name, G., A, 416, Q., A, I, 216 ; 

 " second radial," S.-D., A, II, 359 ; part of the " extenseur anterieur dumetacarpe," Ch., A, 

 277 ; part of the anterior extensor of the metacarpus, Ch. (FI.), A, 262 ; exl. carpi rad. bre- 

 vior, Miv., B, 151. 



Figures. Cephalic aspect, in part (74) ; caudal aspect (75) ; origin area (68). 



General Description. From the epicondylar ridge of the humerus, just proximad of 

 the epicondylus, to the base of the medial metacarpal. 



Dissection. The thicker tendon mentioned as joined with that of the ex. rad. longior 

 belongs to the present muscle. This tendon is shorter than the other, and the body pro- 

 portionately longer, as well as thicker. Divide it 1 cm. farther distad than in the case of 

 the ex. rad. longior, and reflect both ends. 



Origin. By fleshy or short, tendinous fibers from the epicondylar crest, just distad of 



