Page 101 - Anatomy and Physiology of Farm Animals, 8th Edition

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Dorsal Palmar
VetBooks.ir

R U U R

u i r
r i ac 2

2 3 4 4 3 1

V II
II V
III IV IV III

Figure 4-13. Porcine carpus. R, radius; U, ulna; r, radial carpal bone; i, intermediate carpal bone; u,
ulnar carpal bone; 1 – 4, numbered carpal bones; II – V, metacarpals.

on an ancestral four, but among common The pig has four metacarpal bones. The
domestic farm animals only the pig con- first is absent; the second and fifth are
sistently has four carpal bones in this distal reduced in size; and the third and fourth
row. The first carpal bone of the horse, bear most of the weight.
when present, is small and nonweight The digits number one to five, depend-
bearing. The first carpal is not present in ing on the species (Fig. 4‐14). The horse,
ruminants, and the second and third carpal having only one digit, literally walks on the
bones are fused in these species. tip of the middle finger, or third digit. The
The metacarpus is immediately distal digits, like the metacarpal bones, are num-
to the carpus. In the horse it includes a sin- bered from one to five from medial to
gle large metacarpal (cannon) bone, the lateral. Each complete digit is made up of
base for the third digit (corresponding to three phalanges (proximal phalanx, mid-
the middle finger), and two small metacar- dle phalanx, and distal phalanx). In the
pal (splint) bones. The second metacarpal horse, the proximal phalanx is also called
bone is on the medial side, and the fourth the long pastern bone; the middle phalanx
is on the lateral side. Trauma to these small corresponds to the short pastern bone; and
bones with consequent excess bone forma- the distal phalanx is also known as the coffin
tion results in splints. Splints in horses bone. Each digit also includes two proximal
sometimes produce lameness, but often sesamoid bones at the palmar aspect of the
constitute only a blemish, a disfigurement joint between the third metacarpal bone
not usually associated with unsoundness. and proximal phalanx and a distal sesa-
The cannon bone of the ox and sheep is moid (navicular) bone at the junction of
a fusion of the third and fourth metacarpal the middle and distal phalanges.
bones. A vertical groove on the dorsum of Horsemen refer to the joint between the
the cannon bone demarcates the develop- cannon bone and the proximal phalanx
mental line of fusion. (the metacarpophalangeal joint) as the