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 vohir 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 branches pass through the lione to the 

 wall surface and ramify in the matrix of the wall and sole of the hoof. A ninn])er of 

 branch(\s emerge through the foramina at the lower l)ordcr, where they anastomose 

 with 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 l)y a vein and by the digital nerves. Al)ove the 

 fetlock the artery is most deeply placed and is covered by 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 obliquely 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 fibrous basis 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 

 primse), a short trunk 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 fellow. The 

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

 moidean ligaments and anastomoses with the opposite artery. 



2. The artery of the plantar cushion (A. torico} phalangis tertian) 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 phalangis sccunda) 

 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 i)halanx, where 

 it anastomoses with the opposite vessel. It gives branclu>s to the skin, the tendon, 

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



4. The volar artery of the second phalanx (Ranuis volaris jilialangis secunda^) 

 is smaller than the ])rec(Mling, opjiosite to which it arises. It passes al)ove the 

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



The arteries of the second phahmx form wliat is tonnod by Chauveau the coronary 

 circle. Tlie dorsal (anterior) part of the circle f^ivcs off conniionly an artery (A. coronah.s 

 phahinfiis tcr(ia') near oitlicr .side of the extensor tendon, wliich (hvidcs into two liranches. The 

 central l)ranch unites witli tliat 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 ^ome cases de- 

 scending branches of the arteries of the first phalanx concur in tlie formation of the arch. 



5. The dorsal artery of the third phalanx or jirejilantar art(>ry (A. dorsalis phal- 

 angis tertia?) arises at th(> deep face of the wing of the third ])halanx, passes outward 

 through the notcli or foramen there, and nms forward in the groove on the wall 

 surface. It gives off ascending and descending branches, wiiich ramify in the matrix 



