Page 174 - Anatomy and Physiology of Farm Animals, 8th Edition

The Equine Foot and Passive Stay Apparatus / 159

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Figure 8-8. Photomicrographs of a cross‐section of equine fetal hoof in the region of the laminae. Left:
a, corium; b, tubular horn. Right: higher power shows interdigitation of insensitive (darker) laminae with
sensitive (lighter) laminae. Source: photo courtesy of Gretchen Delcambre, Colorado State University,
Fort Collins, Colorado, USA.

The sole of the foot is a concave kerati- from the foot. Deep grooves (collateral
nized plate that attaches to the palmar/ sulci or paracuneal sulci) demarcate the
plantar surface of the third phalanx. sides of the frog from adjacent sole, and a
It includes the entire ground surface of the single central sulcus corresponds to a
foot not occupied by the wall or the frog spine of tissue called the frog stay on the
(see below). Normally, the concavity of the dorsal (deep) side of the frog (Fig. 8‐5).
sole allows the wall and frog to bear most Deep to the frog is the digital cushion, a
of the weight (Fig. 8‐6C). thick wedge of fibrofatty tissue (Fig. 8‐2).
Laypeople and farriers recognize a
narrow band of the deepest part of the
stratum medium, which is typically slightly Tendons
lighter in coloration than the rest of the
hoof wall. This is the white line. The white No muscle bellies extend distal to the car-
line is useful as a landmark for driving nails pus or tarsus in the mature horse. The ten-
in shoeing. A properly directed nail started dons of several muscles continue into the
at or outside the white line will not touch foot, where each tendon inserts on one or
any sensitive structures of the foot. more phalanges, as described in Chapter 7.
The frog (cuneus unguis) is a special- The common digital extensor tendon
ized, wedge‐shaped pad in the center and passes down the dorsal aspect of the metacar-
heel region of the foot’s ground surface. pus, over the fetlock, and inserts on the exten-
The horn of the frog is relatively pliable, sor process of the distal phalanx. The long
and the compression of the frog against the digital extensor tendon has the same course
ground is important for return of blood and insertion in the pelvic limb (Fig. 8‐2).