Page 170 - Anatomy and Physiology of Farm Animals, 8th Edition

The Equine Foot and Passive Stay Apparatus / 155

with the tarsus, and the cannon bone (met- cartilages (collateral cartilages) (Fig. 8‐3).
The dorsal margins of these flexible carti-
atarsal III) articulates distally with the
VetBooks.ir proximal phalanx and the two proximal lages extend proximal to the hoof, where
they are palpable under the skin near the
sesamoid bones. Generally, metatarsal III
is somewhat longer and rounder in cross‐ heels of the foot. Flexibility of the ungual
section than metacarpal III. cartilages probably aids in pumping blood
The three phalanges include: (1) the away from the foot.
proximal phalanx (long pastern bone); Trauma (by either direct injury or
(2) the middle phalanx (short pastern chronic heavy work) may result in ossifi-
bone); and (3) the distal phalanx (coffin cation of the ungual cartilages. This
bone) (Fig. 8‐2). The proximal phalanx produces a condition called sidebone
articulates with the cannon bone at the (Fig. 8‐4). Lameness may or may not
fetlock (metacarpophalangeal and meta- accompany sidebone. Penetrating injury
tarsophalangeal joints) and with the middle in the region of the coronary band may
phalanx at the pastern joint (proximal lead to infection of the ungual cartilage
interphalangeal joint). Middle and distal and the development of chronic draining
phalanges articulate at the coffin joint tracts. This is called quittor.
(distal interphalangeal joint).
The two proximal sesamoid bones lie at
the palmar/plantar surface of the fetlock. Cornified Tissues
The unpaired distal sesamoid (navicular)
bone lies at the palmar or plantar aspect of The hoof is a cornified modification of epi-
the coffin joint. dermis, under which lies a vascular layer,
The distal phalanx features medial and the corium (Fig. 8‐5). The region where
lateral palmar/plantar processes to hairy skin changes to hoof is the coronary
which are attached rhomboidal ungual band (or coronet). The hoof wall is the

Suspensory I.

Fetlock joint

Superficial digital
Pastern joint flexor t.
Common/long digital Deep digital
extensor t.
flexor t.
Coffin joint
Distal sesamoidean II.

“T” ligament
Digital cushion
Navicular bursa
Impar I.
Figure 8-2. Sagittal section of the equine digit. a, metacarpal/metatarsal III; b, proximal phalanx; c,
middle phalanx; d, distal phalanx; e, palmar ligament; f, navicular bone. Note that the extensor tendon on
the dorsal aspect of the digit will either be part of the common digital extensor m. in the forelimb, or of
the long digital extensor m. in the hindlimb. l, ligament; t, tendon.