564 BLOOD-VASCULAR SYSTEM OF THE HORSE 



THE DIGITAL ARTERIES 



The internal and external digital arteries (A. digitalis medialis, lateralis) are 

 formed by the bifurcation of the common digital at the distal third of the meta- 

 carpus. They diverge, pass down over the outer surface of the corresponding 

 sesamoid at the fetlock, and descend parallel with the borders of the deep flexor 

 tendon to the volar grooves and foramina of the third phalanx. Entering the 

 latter the two arteries unite in the semilunar canal and form the terminal arch 

 (Arcus terminalis), from which numerous Ijranches pass through the bone to the 

 wall surface and ramify in the matrix of the wall and sole of the hoof. A number of 

 branches emerge through the foramina at the lower border, where they anastomose 

 Avith each other in arciform fashion. These branches were named by Spooner the 

 inferior communicating arteries, and the anastomotic arch formed by them is 

 termed the circumflex artery of the third phalanx (Chauveau) or the artery- of the 

 lower border of the third phalanx (Leisering). 



Each artery is accompanied by a vein and l^y the digital nerves. Aljove the 

 fetlock the arteiy is most deeply placed and is covered ]:)y the vein; the nerve is 

 behind the vein. At the fetlock the artery has become superficial and is related 

 to the vein in front and the posterior branch of the nerve behind. The anterior 

 branch of the nerve crosses over the artery ol^liquely to the lateral aspect of the 

 first phalanx. The vessels and nerves are crossed obliquely by a small tendinous 

 band, the ligament of the ergot, which begins in the fil;)rous liasis of the ergot at 

 the back of the fetlock and extends downward and forward to end in the fascia at 

 the side of the pastern joint. 



In addition to branches to the joints, tendons and synovial sheath, ergot, and 

 skin, the digital arteries give off: 



1. The artery of the first phalanx or perpendicular artery (A. phalangis 

 prima?), a short trimk which arises at a right angle about the middle of the first 

 phalanx, and divides into dorsal and volar branches (Rami dorsales et volares). 

 The dorsal (anterior) branch passes between the first phalanx and the extensor 

 tendon and ramifies on the front of the digit, anastomosing with its fellows The 

 volar (posterior) branch dips in lietween the flexor tendons and the inferior sesa- 

 moidean ligaments and anastomoses with the opposite artery. 



2. The artery of the plantar cushion (A. toricse phalangis tertia?) arises at the 

 proximal border of the lateral cartilage and passes backward and downward to 

 ramify in the plantar cushion and the matrix of the heels and frog. 



3. The dorsal artery of the second phalanx (Ramus dorsalis jjhalangis secundir) 

 arises a little above the navicular bone, and passes forward under cover of the 

 lateral cartilage and the extensor tendon to the front of the second phalanx, where 

 it anastomoses with the opposite vessel. It gives branches to the skin, the tendon, 

 the coffin joint, and the coronary matrix of the hoof. 



4. The volar artery of the second phalanx (Ramus volaris phalangis secund^e) 

 is smaller than the preceding, opposite to which it arises. It passes above the 

 proximal border of the third sesamoid and unites with the opposite artery. 



The arteries of the second phalanx form what is termed by Chauveau the coronary 

 circle. The dorsal (anterior) part of the circle gives off commonly an artery (A. coronalis 

 phalangis tertia?) near either side of the extensor tendon, which divides into two branches. The 

 central branch unites with that of the opposite side, while the other joins a branch of the artery 

 of the plantar cushion. In this way is formed the circumflex artery of the coronary cushion, 

 an anastomotic arch which lies on the extensor tendon at the coronet. In .some cases de- 

 scending branches of the arteries of the first plialanx concur in the formation of the arch. 



5. The dorsal artery of the third phalanx or preplantar artery (A. dorsalis phal- 

 angis tertise) arises at the deep face of the wing of the third phalanx, passes outward 

 through the notch or foramen there, and runs forward in the groove on the wall 

 surface. It gives off ascending and descenchng branches, which ramify in the matrix 



