35 2 



PRACTICAL ANATOMY. 



index finger, it is necessary for the student to trace each muscle to its specific 

 origin and insertion according to the following scheme for aiding the memory : 



The extensor indicis (Fig. 245') arises practically from the posterior surface 

 of the lower one-third of the ulna and interosseous membrane. Demonstrate on 

 the cadaver the amount of ulnar surface in the lower third of the bone which 



Triceps 



Lower limit of orbicular ligament 



Grooves for extensor ossis, and extensor 

 primi internodii pollicis 



For extensor carpi radialis longior 



and brevior 

 Extensor secundi interuodii pollicis 



Extensor primi interuodii pollicis 



SUBCUTANEOUS SURFACE 



Extensor ossis metacarpi pollicis 



AN APONEUROSIS IS ATTACHED TO THIS BORDER 

 FROM WHICH THE flexor AND extensor 

 carpi vliaris, AND flexor profundus 

 digitorum ARISE 



Extensor sccundi internodii pollicis 



ULNA 

 Extensor indicis 



Extensor minimi 

 Extensor carpi ulnaris 



Internal lateral ligament 



Extensor communis digitorum Posterior Posterior radio-ulnar ligament 

 and extensor indicis radio-carpal 



ligament 



FIG. 246. THE LEFT ULNA AND RADIUS. (Postero-external view.) 



does not give origin to this muscle. Observe, too, the septal origin of the 

 muscle, between this and the extensor longus pollicis. 



Now consider the origins of the three' extensors of the thumb in reference to : 

 (i) The posterior surface of the radius ; (2) the posterior surface of the ulna ; 

 (3) the posterior surface of the interosseous membrane. Notice, too, you have 

 to deal with a long hone, the ulna ; a short bone, the radius ; and an interosseous 



