612 TEE VEINS. 



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

 vessel lodged with the plantar interosseous arteries between the suspensory 

 lieament and the posterior face of the principal metacarpal bone. Eeaching 

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

 with the external and internal collaterals, sending upwards one or two small 

 branches which traverse the carpal sheath along with the collateral artery 

 of the cannon, and open 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 terminate in uniting above the fetlock, between the flexor tendons of the 

 phalanges and the superior sesamoid ligament, so as to form an arch from 

 which proceed the three metacarpal veins (Fig. 293, 37). 



8. Veins of the Foot or Ungual Begion. 



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.i 



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 

 marvellously displayed in specimens injected after maceration, and then 

 dried. 



" To facilitate its description, we recognise in it three parts distinct by 

 their situation, though they only form a continuous one. They are : 



" 1. The solar plexus. 



"2. The podophyllous plexus. 



" 3, The coronary plexus. 



" A. Solar Plexus. — The veins of the solar plexus are remarkable for 

 the equality of their calibre throughout the whole extent of the plantar 

 surface, and by the almost absolute absence of anastomotic communications 

 with the deep parts. 



" Sustained in a special fibrous web (plantar reticulum), which replaces 

 the periosteum at the lower surface of the phalanx, and is a continuation of 

 the cerium of the villous tissue, these veins appear indeed to have so little 

 communication, except with each other, that it is possible to detach the 

 plantar reticulum from the superior face of the third phalanx without 

 disturbing them. 



' ' Traite de 'Organisation du Pied du Cheval,' p. 65. 



