178 THE SURGICAL ANATOMY OF THE HORSE 



branches, which are distributed to the flexor tendons and the inferior 

 sesamoidean Hgaments. The perpendicular artery terminates on the lateral 

 aspect of the os sufFraginis by splitting into two terminal divisions. 

 One of these ascends and may extend to the fetlock joint. The other 

 takes a downward course to the lateral aspect of the os corons, where it 

 joins the coronary circle. 



The terminal ramifications of the perpendicular artery anastomose 

 with those of the corresponding artery of the opposite side on the 

 anterior and posterior aspects of the first phalanx, which is thus sur- 

 rounded by a network of tiny vessels. 



3. 'The Artery to the Plantar Cushion. — This vessel leaves the digital 

 artery near the upper border of the lateral cartilage, and passes downwards 

 and backwards to the plantar cushion. It will be further described when 

 dealing with the foot. 



4. The Coronary Circle. — Two transverse branches arise from each 

 digital artery on the inner aspect of the corresponding lateral cartilage. 

 The anterior branches pass forwards and anastomose with one another on 

 the anterior face of the os corons under cover of the expanded portion 

 of the tendon of the extensor pedis. The posterior branches pass round 

 the back of the corona, where they anastomose on the deep face of the 

 perforans tendon just above the superior border of the navicular bone. 

 There is thus formed a complete arterial circle around the second 

 phalanx. 



THE VEINS 



The Digital Veins. — From the venous plexuses of the foot, which will 

 be described when dealing with that part, the blood is drained by the 

 two digital veins. Each digital vein passes up the limb in front of the 

 corresponding digital artery, from which it is usually separated by the 

 middle digital nerve. Above the point of detachment of this nerve the 

 vein is in immediate relationship to the artery, in front of which it 



