19 



arch, the A. metacarpa volaris lateralis runs in a flexuous course on the 

 posterior face of the large metacarpal bone, close to the lateral rudi- 

 mentary metacarpal. Near the distal third of the metacarpus the artery 

 unites with the A. metacarpea volaris medialis to form a short trunk which 

 joins the A. digitalis lateralis close to the origin of the latter. 



A. metacarpea volaris medialis (PI. Ill, 17) arises from the radialis posterior, 



usually a little proximal to the metacarpea volaris lateralis, and is con- 

 siderably larger than that artery. It passes across the postero-internal 

 face of the carpus with the large vein of the same name, imbedded in the 

 carpal sheath or posterior annular ligament. At the proximal end of the 

 internal rudimentary metacarpal it is connected with the A. metacarpea 

 volaris lateralis, usually, by two transverse branches (arcus volaris pro- 

 fundus) as mentioned above. It then continues in a flexuous course, on 

 the posterior internal face of the large metacarpal, to near the distal third 

 of the metacarpus where it unites with the metacarpea volaris lateralis 

 to form a short common trunk which joins the A. digitalis lateralis. The 

 nutrient artery of the large metacarpal bone is a branch of the metacarpea 

 volaris medialis. 



A. metacarpea dorsalis lateralis and A. metacarpea dorsalis medialis are 



two very small arteries that have a variable origin. Sometimes they arise 

 from the A. metacarpea volaris, of the same side, at the level of the deep 

 vascular arch. They extend anteriorly across the heads of the rudimentary 

 metacarpals, descend in the grooves between the large and small metacarpal 

 bones, and anastamose with the corresponding A. metacarpea volaris. 

 Sometimes these two small arteries arise from the rete carpi dorsalis and 

 in other cases, they arise in part from the rete carpi dorsalis and in part 

 from the A. metacarpea volaris lateralis and the A. raetacarpea volaris 

 medialis. 



A. digitalis communis (PI. Ill, 18) is the largest and most direct continua- 

 tion of the A. radialis posterior. It extends through the carpal canal at 

 the medial side of the flexor tendons, in company with the N. volaris 

 medialis. Slit open the carpal canal and trace the artery and the large 

 metacarpal vein that, in the metacarpal region, accompanies the artery 

 along the medial side of the flexor tendons to near the fetlock where the 

 artery divides into the A. digitalis lateralis and the A. digitalis medialis. 

 Remove the hoof or horn capsule. 



N. volaris medialis (PI. Ill, 27) is formed by one of the terminal branches of 

 the N. medianus. It passes through the carpal canal in close company with 



