638 THE ARTERIES. 



portions of the metacarpo-phalangeal articulation, the digital artery is crossed 

 from behind to before by the anterior branch of the plantar nerve, and it is 

 covered for the whole of its extent by the fascia that continues the proper tunic 

 of the plantar cushion, the lateral ligamentous band of which cuts its direction 

 obliquely downwards and forwards, at the middle portion of the first phalanx." ^ 

 Collateral divisions. — These are: 1. At the fetlock, numerous fine branches 

 distributed to the metacarpo-phalangeal articulation, but particularly to the 

 sesamoid sheath and the tendons lodged in it. 



2. To the environs of the upper extremity of the first phalanx, slightly 

 ascending and sometimes voluminous twigs, for the tissue of the ergot (the horny 

 tubercle behind the fetlock). 



3. Towards the middle of the same bone, the vessel named by Percivall the 

 perpendicular artery, and correctly so, for it^ arises at a right iingle from the 

 digital artery to divide almost immediately afterwards into two series of ramifi- 

 cations — anterior and posterior. The anterior branches are in nearly every 

 instance two principal : one ascending, passing beneath the check-band of the 

 extensor tendon, and climbing to the capsular ligament of the fetlock-joint to 

 meet the arterial divisions furnished directly to that ligament by the collateral 

 artery of the cannon ; the other descending, which reaches the side of the 

 second phalanx, where its ramuscules anastomose with the coronary circle and 

 the circumflex artery of the coronary cushion. The posterior ramifications 

 consist most frequently of two principal branches — one ascending, the other 

 descending ; these insinuate themselves between the flexor tendons and the 

 sesamoid ligaments, to be distributed to these organs, but especially to the syno- 

 vial membrane of the large sesamoidean bursa. Sometimes it is seen to arise 

 alone from the digital artery. It must here be noted, that the divisions 

 furnished by the anterior branches of this perpendicular artery communicate 

 with those of the opposite side in front of the first phalanx, either above or 

 below the principal extensor of the digit ; and that the posterior branches 

 exhibit a series of analogous anastomoses. The body of the first phalanx is 

 therefore enveloped on every side by an arterial plexus. 



4. At different elevations on the first and second phalanges, several tendinous 

 and cutaneous twigs, which are of no importance. 



5. The artery of the plantar cushion, which arises at the superior border of 

 the lateral cartilage, is directed obhquely backward and downward, and placed 

 within the posterior border of that cartilage, to be distributed to the middle 

 portion of the complementary apparatus of the third phalanx, as well as to the 

 villous tissue and the coronet. The branch expended in the latter sometimes 

 proceeds directly from the digital artery ; it is a very remarkable vessel, is 

 inflected from before to behind, crossing the posterior border of the pedal carti- 

 lage, creeping on the internal face or in the texture of the skin, a little above the 

 coronet, parallel with that portion of the keratogenous apparatus, and terminates 

 by anastomosing with a branch of the artery now to be noticed. 



6. The coronary circle^^ formed by two transverse branches — one anterior, the 

 other posterior, springing at a right angle from the digital artery, under the 

 cartilaginous plate of the os pedis — passes around the coronary bone to meet 

 the analogous branches of the opposite artery, to anastomose with them directly 

 and by inosculation. The coronary circle therefore presents two distinct por- 



' H. Bouley, Traite de V Orcfanimtion du Pied du Cheval. Paris, 1851. 

 * So named because it encircles tlie coronet. 



