The accompanying illustration (fig. 655) will show that in many respects it is possible to compare the bony framework of the horse with that of man, in whose structure the highest type of anatomical mechanism is exhibited.

For the general reader the most interesting feature in the illustration will be the arrangement of the joints of the limbs of the horse in comparison with those of man, and a very little study of the engraving will correct some popular errors, such, for instance, as refer to the position of the knee of the horse. The real knee of the animal is, in the phraseology of the horseman, the stifle-joint, and the joint which is usually called the knee of the horse is in reality the wrist. The letters in the illustration indicate the true shoulder, elbow, wrist, hip, knee, and ankle in both man and horse.

Commencing with the fore parts of the skeleton, we will first notice the joint which is called the wrist or carious, the knee of the horse as it is wrongly named. In this two rows of small bones are arranged, as can be seen in the figure, between the arm-bone above and the shank-bones below, the latter consisting of one large bone and two small splint-bones attached to it. In man the corresponding arrangement conduces to a very important end - a series of movements in the hand and arm which are mechanically impossible in the horse, notwithstanding the apparent similarity of structure.

Comparative View of Skeletons of Man and Horse.

Fig. 655. - Comparative View of Skeletons of Man and Horse.

S, Shoulder-joint; E, elbow-joint; w, wrist-joint (so-called knee in the horse); H, hip-joint; K, knee (stifle-joint in the horse); A, ankle (hock-joint in the horse).

The hand of man constantly performs the movements of flexion and extension, as they are called (these being hinge-like motions with extensive lateral movement), and in addition almost perfect rotation, at least to the extent of two-thirds of the circle. On the other hand, the horse's wrist or knee is only capable of flexion and extension.

Nearly the same degree and exactly the same variety of movement are possible in the elbow-joint of man, while in the horse, owing to the rudimentary form of the second bone of the arm (the ulna), no lateral or rotatory motion can take place. The movement is purely hinge-like.

Another marked peculiarity is observed in the connection of the shoulder-blade (scapula) with the trunk. In man the junction is effected by a bone known as the collar-bone (or clavicle), which extends from the shoulder-bone near the shoulder-joint to the first rib on each side. The horse has no vestige of a collar-bone; the shoulder-blade (scapula) is joined to the trunk only by means of the muscles which are attached to it, so that the fore part of the horse's body is suspended by the aid of muscular bands between the two fore-legs.

An examination of the hinder limbs will show that the general plan of construction is nearly the same in both man and horse, as far as the joints are concerned. The hip-joint, the stifle (the true knee) with the floating bone or knee-cap (patella), and the hock (ankle of man) are almost identical in mechanical arrangement.

With regard to the hock-joint it may be observed that the two rows of small bones are placed as in the ankle of man, but the movement of the joint is purely hinge-like, and experience proves that the two rows of small bones may be cemented together, and to the cannon-bones and splint-bones below them, by bony deposits in old horses without causing any defect in the action - to a sufficient extent, at least, to be noticed. In fact, the provision for perfectly complete flexion in the hock-joint is secured by the mode of junction of the bones called tibia and astragalus (see fig. 658). The so-called cushion bones do not appear to contribute much, if anything, to the mobility of the joint, in the flexion and extension of which the small bones are largely concerned.

Below the knee in front, and the hock behind, begins the hand and foot respectively. The one large digit in each extremity, composed of what are called the metacarpal and metatarsal bones; the rudimentary second and fourth digits (the splint-bones) attached to them, and reaching two-thirds of their length, and the three following phalanges, constitute the true hand and foot. The horse, in fact, stands on those parts which in man form respectively the tip of the middle finger and the point of the middle toe, both of which are capped with an investing hoof instead of a nail.

The next illustration shows the exact relation between the finger of man and the reputed foot of the horse. How very close the anatomical relation is will be at once evident.

The chief anatomical difference between the fingers of man and the foot of the horse (which represents the end of the middle finger) consists in the presence of - (l) a complete horny box or hoof, which covers the organ in the horse; (2) the three floating bones or sesamoids, of which two are attached to the back of the lower end of the metacarpal bone and one navicular behind the last phalanx, or rather between it and the articular end of the bone immediately above it, the coronal bone or short pastern.

Section of Finger of Man.

Fig. 656. - Section of Finger of Man.

1. Metacarpal bone.

2. First phalanx.

3. Second phalanx.

4. Third or ungual phalanx (pedal bone of horse). (5-6 wanting).

7. Tendon of extensor muscles.

8. Tendon of superficial flexor (flexor perforatus).

9. Tendon of deep flexor (flexor perforans). 11 and 14. Derma or true skin.

15. Nail (imperfect hoof of horse).

17. Fibro-fatty cushion of end of finger.

18. Fibro-fatty cushion of palm behind metacarpal phalangeal joint.

19. Thickened epidermal covering of the same.

Section of Foot of Horse.

Fig. 657. - Section of Foot of Horse.

1. Metacarpal bone.

2. First phalanx.

3. Second phalanx.

4. Third or ungual phalanx.

5. One of the upper sesamoid bones.

6. Lower sesamoid or navicular bone.

7. Tendon of extensor muscle.

8. Tendon of superficial flexor (flexor perforatus).

9. Tendon of deep flexor (flexor perforans).

10. Short flexor or suspensory ligament of the fetlock.

11. Derma or true skin continued into.

12. Coronary cushion.

13. 14. Villous portion of the hoof matrix.

15. Hoof.

16. The heel.

17. Plantar cushion.

18. Fibro-fatty cushion of the fetlock.

19. Horny excrescence or spur (ergot).

In the human hand two sesamoid bones are found where the thumb articulates with the first metacarpal bone on the inner or palm surface. None exists elsewhere in the hand.

When we give full weight to the points of difference in the fore-limbs of the horse, as compared with the upper (fore) extremity of man, the similarity in the details of the plan of construction in both man and horse must seem far more striking than the variations, and this fact, taken in connection with the marked difference in the position and general functions of the fore extremities in each subject, is certainly more suggestive of evolution than of special design. Unless on the theory of evolution from remote ancestors, it is indeed unintelligible that all the bones of the carpus (wrist) of man, conducing as they do to the greatest perfection of complicated movements, should be represented in the same joint (knee) of the horse, but so modified in their arrangement as to permit of no more than a simple hinge-like motion, which is quite effectually provided for in other hinge-joints by the adaptation of two bones only. And again, some of the digits of man, one of the five-fingered and five-toed mammals, are represented in the horse by undeveloped structures or rudiments which serve no useful purpose, as the horse walks on the tip of a single finger and a single toe; in the foot of man, on the contrary, the whole of the bones from the ankle-joint are brought into use, forming the plantar surface or sole. Such a modification of structure in the lower animal can be understood only on the assumption that it was the result of a gradual process of development through which the five-toed foot of the horse's remote ancestors was in course of ages transformed to the one-toed foot of the horse as we now know it. A very pronounced series of changes it must be allowed, the true character of which will be more easily understood by reference to figs. 658 and 659, taken by permission of the Royal Agricultural Society from an article on the structure of the horse's foot by Professor Sir Geo. T. Brown, and published in the Society's Journal, 1891.

Foot of Man and Foot of Horse Compared in Natural Positions (Note position of ground surface in each case).

Fig. 658. - Foot of Man and Foot of Horse Compared in Natural Positions (Note position of ground surface in each case).

A, Tibia. B, Astragalus, c, Calcis. D, Scaphoid. E, Internal cuneiform. F, Splint-bone (a vestige of 2nd metatarsal). G, Cannon bone, or 3rd metatarsal. 1, 2, 3, Phalanges.

In fig. 658 both man and horse have the foot placed as it is in nature.

Man presents the entire under surfaces of the bones of the tarsus (hock of the horse), with the metatarsal bones and the four phalanges, to the ground surface, while the horse stands on the fourth or terminal phalanx. Fig. 659 shows the positions reversed; the foot of the man has the points of the toes on the ground in a position corresponding to that which is natural in the horse, and the horse is supposed to be in the impossible position of having the whole of the bones from the point of the hock to the last phalanx of the toe on the ground as in the foot of the man. The teaching of the diagram is that for the horse to exhibit a perfect foot, the bones below the carpus (knee) and the tarsus (hock) would have to be included in the structures of the organ; instead of this being the case, it is obvious that what is called the foot of the horse only includes the two last phalanges.

Foot of Man and Foot of Horse Compared (positions reversed) (Note position of ground surface in each case).

Fig. 659. - Foot of Man and Foot of Horse Compared (positions reversed) (Note position of ground surface in each case).

The names of the several bones are given below fig. 658 on the preceding page.

It will be noticed in comparing the above illustrations with the skeletons in fig. 655, page 486, that in man the bones of the leg (the tibia and fibula) up to the knee, and the thigh-bone (femur) from the knee to the hip-joint, form a column which is nearly a straight line. The limbs of the horse, on the contrary, present very decided angles at several points, chiefly at the shoulder, elbow, hip, stifle, and hock joints; and also from the fetlock-joints to the ground surface, an arrangement which is eminently calculated to give freedom of movement, and at the same time lessen the effect of concussion.