Limb Vasculature - Horse Anatomy

Thoracic Limb Arteries

Digit and Fetlock

The arterial supply to the digit and fetlock of the thoracic limb comes mainly from the median palmar artery. The median palmar artery divides in the distal fourth of the metacarpus, between the superficial and digital flexor tendons and the suspensory ligament, to become the medial and lateral digital arteries. Part of the deep palmar arch anastamoses with the lateral digital artery to form the superficial palmar arch, which supplies the fetlock joint.

The digital arteries run superficially in the proximal fetlock region, emerging palmar to their satellite vein and between the palmar digital nerve and its dorsal branch. The medial and lateral digital arteries run distally over the fetlock and each branches to supply the fetlock joint, digital extensor and flexor tendons, digital sheath, ligaments fascia and skin.

The short artery of the proximal phalanx arises from the medial and lateral digital arteries, immediately dividing into dorsal and palmar branches to form a circle around the middle of the proximal phalanx. This supplies the proximal phalanx and surrounding structures. The palmar branch of the short artery runs between the proximal phalanx and the digital flexor tendons to join the contralateral vessel between the sesamoidean ligaments. The dorsal branch joins the contralateral vessel deep to the common digital extensor tendon.

In the region of the proximal interphalangeal (pastern) joint, the bulbar artery (artery of the digital cushion) arises from each digital artery. This artery branches to supply the frog, digital cushion, palmar part of the cuneate corium, laminar corium of the heel and bar and palmar parts of the perioplic and coronary corium.

The coronal artery arises from the digital artery or the bulbar artery to supply the heel and perioplic corium. The coronal artery then anastamoses with branches from the dorsal artery of the middle phalanx. The dorsal artery of the middle phalanx arises from each digital artery in the mid-region of the middle phalanx, forming the coronary arterial circle; as the palmar and dorsal branches anastamose to form a complete arterial circle around the middle phalanx. This coronary arterial circle supplies the distal interphalangeal (coffin) joint, common digital extensor tenon, perioplic and coronary corium, fascia and skin.

Branches from the conjoined palmar branches of the middle phalanx anastamose to form the navicular plexus, providing several small arteries to foramina along the proximal border of the distal sesamoid (navicular) bone. This plexus provides approximately one third of the total blood supply to the navicular bone.

At the level of the palmar process of the distal phalanx, the digital artery forms a dorsal branch of the distal phalanx, then continues distally to the terminal arch. The dorsal branch gives off a small artery to supply the digital cushion and corium of the frog, before it passes through a foramen in the palmar process of the distal phalanx. It then bifurcates on the dorsal surface of the distal phalanx to form branches that supply the corium of the heels and quarters, laminar corium of the toe, and eventually joining branches of the coronal artery and the marginal artery of the sole. The termination of the dorsal branch of the distal phalanx joins with a vessel that comes from the terminal arch in the solar canal. It then branches into several small arteries which enter the distal border of the distal phalanx.

The medial and lateral digital arteries run in the solar groove of the distal phalanx. Each gives off branches to the navicular plexus in the distal sesamoidean (impar) ligament. The navicular plexus gives rise to the distal navicular arteries, which enter the distal sesamoid (navicular) bone at the distal border and anastamose within the foraminae of the bone. These distal navicular arteries supply the distal two thirds of the navicular bone.

The medial and lateral digital arteries enter the solar foramen and form the terminal arch within the solar canal of the distal phalanx. Branches from the terminal arch run through foraminae on the parietal surface of the distal phalanx to supply the laminar corium. Several of these branches emerge near the solar border and anastamose to form the marginal artery of the sole. This supplies the solar and cuneate corium.

The arterial supply to the digit in the pelvic limb is the same as in the thoracic limb, except for the supply to the navicular bone. In the pelvic limb of some horses, a collateral arch from the plantar branches of the middle phalanx supply the proximal navicular network.