THE LIMBS OF THE HOKSE 35 



there is no difficulty in showing that it blends with the ligaments and 

 the periosteum of the bone. 



The tensor fascia 1 antibrachii is mainly inserted into the fascia, with 

 which also certain fibres of the brachiocephalic and biceps muscles are 

 connected. 



A definite compartment for the extensor digiti quinti is formed by 

 the fascia sinking in between this muscle and its immediate neighbours 

 to form intermuscular septa. Similar septa will be found elsewhere, as, 

 for example, between the radial extensor of the carpus and the common 

 extensor of the digits, and between the radial and ulnar flexors of the 

 carpus. Furthermore, the deep fascia is strengthened by transverse 

 fibres to form the dorsal carpal ligament (ligamentum carpi dorsale) 

 that retains the extensor tendons in the grooves at the distal end 

 of the radius. 



But the most conspicuous thickening of the fascia occurs over the 

 volar aspect of the carpus where the strong transverse carpal ligament 

 (ligamentum carpi transversum) forms a stout bridge from the accessory 

 carpal (pisiform) bone to the medial collateral ligament and the proximal 

 end of the second metacarpal bone. The transverse ligament con- 

 stitutes the volar boundary of a short canal in which are contained the 

 flexor tendons with their synovial sheaths, the common digital artery, 

 and the medial volar nerve. 



Dissection. — Remove the deep fascia over the extensor muscles and 

 proceed with their examination. 



The extensor muscles in front and on the lateral aspect of the fore- 

 arm are arranged in two layers, superficial and deep. The superficial 

 layer contains the extensor carpi radialis, extensor digitorum communis, 

 extensor digiti quinti, and extensor carpi ulnaris — in this order from 

 the radial to the ulnar border of the limb. The deep layer in the horse 

 contains one muscle only, namely, the m. abductor pollicis longus. 



M. extensor carpi radialis. — In man and in the dog the radial 

 extensor of the carpus 1 is divisible into two portions — long and short ; 

 but in the horse no such division is possible. A powerful muscle with 

 a prominent and distally tapering belly, the radial extensor takes its 

 main origin from the lateral epicondyle of the humerus. In addition, 

 part of its tendinous origin is from the coronoid fossa in common with 

 the common extensor of the digits. It will be observed that the muscle 

 at its origin has some of its fibres disposed in a curved manner as 

 a consequence of their attachment to a strong fascia overlying the 

 brachialis muscle. Note also the strong tendinous slip (lacertus 2 



1 Carpus [L.], Kapiros (carpos) [Gr.], the wrist. 



-Lacertus [L.], the arm, from the shoulder to the elbow ; a lizard. 



