130 



DISSECTION OP THE DOG 



lodged are produced. The arrangement of the tendons may be summarised 

 in the following manner : 



ULNAE. 



■5b 



s a 



•a 





s s 



RADIAL. 



The muscles in front and on the lateral aspect of the forearm are arranged 

 in two layers, superficial and deep. The superficial layer contains the 

 mm. brachio-radialis, extensor carpi radialis, extensor digitorum communis, 

 extensor digiti tertii et quarti, extensor digiti quinti, and extensor carpi 

 ulnaris — in this order from the radial to the ulnar border of the forearm. 



M. brachio-radialis. — The brachio-radial muscle is very often exceed- 

 ingly rudimentary or even absent, and lies immediately under the skin 

 superficial to the radial extensor. 



The origin of the muscle is from the proximal part of the ridge above the 

 lateral epicondyle of the humerus, and its insertion is into the medial border 

 of the radius. 



M. extensor carpi radialis. — This, the most bulky muscle in front of 

 the forearm, has origin partly from the lateral epicondyle of the humerus, but 

 mainly from the ridge proximal to the eminence. The fleshy belly of the 

 muscle lies lateral to the brachialis and is imperfectly divided into two layers. 

 The superficial layer gives place to a flattened tendon which is inserted into 

 the base of the second metacarpal bone (m. extensor carpi radialis longus). 

 The deep part of the muscle, larger and longer than the preceding, is succeeded 

 by a strong tendon which terminates at the base of the third metacarpal bone 

 (m. extensor carpi radialis brevis). The two tendons are crossed obliquely in 

 the distal third of the radius by the abductor polhcis longus, and are held down 

 in a broad groove at the distal end of the radius by the annular ligament. 



M. extensor digitorum communis. — The common extensor muscle of 

 the digits is lateral to the foregoing, with which it is intimately connected at 

 its origin from the lateral epicondyle of the humerus and from the septum 



