STRUCTURE AND DISEASES OF THE HORSE’S FOOT. 359 
stant. Whatever parts are dropped are from the sides, with correspond- 
ing modifications of the carpal and tarsal elements. This dropping of 
digital elements to contribute to greater simplicity of structure is not 
confined to the foot of the horse; indeed, it has its most complete mani- 
festation short of obliteration in this animal, but is seen to a less extent 
in other animals. Taking five toes as the highest number present in 
any land mammal, we have a reduction to four in the hippopotamus, to 
three in the rhinoceros, and two in the ox. The elements not used are 
frequently present in rudimentary form, as seen in the splint-bones of 
the horse and the two small toes in the ox and hog. Fossil skeletons 
of horses-show that in previous geological eras horses have lived having, 
in addition to the fully developed single digit, two others, perfect as to 
form, but smaller in size. 
The anatomical foot of quadrupeds consists of all the parts beyond the 
radius, or radius and ulna, of the anterior extremities, and the tibia, or 
tibia and fibula, of the posterior. This would include the carpal bones, 
(the knee,) and the bones below, of the anterior, and the tarsal bones, 
(the hock,) and bones below, of the posterior extremities. In point of 
iact, however, uses considered, the foot of the horse is much more limited 
in its extent, including only the terminal phalanx—Fig. 2, “p. 3,” a 
portion of the middle phalanx *‘p.2” and a sesamoid bone, the navicular, 
at the posterior aspect of the joint between the two. (Fig. 14,* “2,” 
3,” “4.”) Below the carpus (igs. 3+ and 4f, ‘“a”) of the anterior, the 
tarsus (Figs. 5§ and 6||) of the posterior extremities, the bones of the. 
leg have similar common names, and are essentially alike in correspond- 
ing regions. Immediately below the carpus and tarsus is a single large 
metacarpal or metatarsal bone, called the cannon-bone, (Figs. 3, 4, 5, 6.) 
Upon either side of this is a rudimentary bone, the splint-bone, (see 
Figs. 4, 5, 6, and 7.) These two splint bones, expanded at their 
upper extremities, where they enter into the formation of the knee 
and hock joints, grow gradually smaller as they pass down by the side, 
and rather to the rear of the main bone, and terminate before reaching 
the fetlock joint. Below the cannon-bone, taking an oblique direc- 
tion anteriorly from it, is the pastern-bone, (igs. 3, 4, 5, 6, and 8,) 
(long pastern, os suffraginis.) In length it is from one-third to one- 
half that of the cannon-bone. Below this is the coronet-bone, (Figs. 
3, 4, 5, 6, 9,) (short pastern,. lower pastern, os corone,) which is nearly 
square in form; its transverse diameter being, however, greater than 
its vertical. The last bone terminating the extremity is the cofin-bone, 
(Figs. 5, 4, 5, 6, and 10,) (os pedis.) This bone is deseribed as having a 
body and wings. Its general outline is semilunar anteriorly, superiorly 
it is convex, and posteriorly and inferiorly it is concave. In texture 
it is light and spongy, perforated throughout by canals, (Figs. 16] and 
*¥ig. 14.—Vertical section of the foot of the horse, copied from Owen: J; pastern- 
bone; 2, coronet-bone; 3, navicular bone; 4, coflin-bone; 5, extensor tendon ; 6, part 
of common flexor tendon; 7, deep flexor tendon; 8, posterior expansion of great 
cartilage; 9, soft cushion of the heel; 10, section of horny hoof; 11, sensitive hoof; 
12, anterior section of the cartilage spreading over the coffin-bone, ; 
t Fic. 3.—Bone of fore leg, front view: a, bones of carpus; b, cannon-bone ; ¢, pastern- 
bone; d, coronet-bone; e, coffin-bone. ° 
-{Fia. 4.—Bones of fore leg, side view: a, bones of carpus; b, splint-bone ; c, cannon- 
bone; d, sesamoid bone; e, pastern-bone; 7, coronet-bone; g, coffin-bone. 
§ Fic. 5.—Hind leg, front view: a, b,c, d, e, bones of the tarsus; f, cannon-bone; 
g, pastern-bone ; h, coronet; 2, coffin-bone. 
|| Fra. 6—Hind leg, side view: a, bones of the tarsus; b, splint-bone ; ¢c, cannon-bone; 
d, sesamoid bone; e, pastern-bone ; f, coronet-bone; g, coffin-bone. 
{i F1c. 16.—Posterior view of the coffin-bone, showing the openings into the interior 
canals, through which branches of the plantar arteries and veins enter: 4, a, a, a, en- 
trance to canals. 
