698 THE VEINS 



6. Metacarpal Veins. 



Three in number, these veins are distinguished into internal and externa), 

 metacarpals or collaterals of the cannon, and deep or interosseous metacarpal or 

 collateral. 



A. Internal Metacarpal Vein. — More voluminous than the others, tliis vein 

 passes from the vicinity of the fetlock along the flexor tendons, accompanied by 

 the principal artery of the cannon and the externri plantar nerve, places itself in 

 the special sheath which envelops the common trunk of the interosseous arteries 

 to the inside of, and behind the carpus, to be continued in the antibrachial 

 region by the internal subcutaneous vein, after communicating with the other 

 metacarpal veins (Fig. 389, 30). 



B. External Metacarpal Vein. — Situated opposite the preceding— to the 

 external side of the flexor tendons, in company with the corresponding plantar 

 nerve — this vessel follows that nerve to near the supra-carpal, and then separates 

 into several reticulate branches which anastomose with the internal vein, from 

 which proceed the ulnar and internal or posterior radial veins. 



C. Interosseous Vein. — A tortuous, irregular, and sometimes multiple 

 vessel, lodged with the plantar interosseous arteries between the suspensory 

 ligament and the posterior face of the principal metacarpal bone. Reaching the 

 superior extremity of that bone, it unites largely to the right and left with the 

 external and internal metacarpals, sending upwards one or two small branches 

 which traverse the carpal sheath along with the collateral artery of the cannon, 

 and enter into the posterior radial branches above the knee. 



7. Digital Veins. 



These veins occupy, on the sides of the digital region, the same position as 

 the homonymous arteries in front of which they are placed They arise from 

 the network formed on the lateral cartilages by the veins of the foot, and termi- 

 nate in uniting above the fetlock, between the flexor tendons of the phalanges 

 and the suspensory ligament, so as to form an arch (the sesamoidean) from which 

 proceed the three metacarpal veins (Fig. 389, 37). 



8. Veins of the Foot or Ungual Region. 



The importance of the region to which these vessels belong, requires that 

 they should be described more fully than the other veins, and as has been 

 already done with the arteries of this part of the body. We will, therefore, 

 borrow the exact and minute description given by M. H. Bouley.^ 



This venous apparatus may be divided into external and internal or intra- 

 osseous. 



a. External Venous Apparatus. 



" The external venous apparatus of the digital region is very remarkable for 

 the number, development, superficial distribution, and reticulated disposition of 

 the canals composing it. To give an idea of this, we cannot do better than 

 compare its general form to a net whose irregular meshes are extended over, and 

 moulded on, the two last phalanges which are contained in it. 



" This intricate reticulation of the venous apparatus of the foot is marvel- 

 lously displayed in specimens injected after maceration, and then dried. 

 ' Traiti de V Organization du Pied du Cheval, p. 65. 



