RUDIMENTARY ORGANS. 91 



there is the humerus (h\ or bone of the horse's upper arm, concealed, 

 however, beneath the skin and muscles, and being, therefore, incon- 

 spicuous in the living animal. The horse's fore-arm, like that of 

 man, contains two bones radius (r) and ulna (u), it is true ; 

 but the ulna has degenerated in a marked degree, and exists as 

 a mere strip of bone which is tolerably distinct at its upper end, 

 but unites with and merges into the other 

 bone, the well-developed radius. The wrist 

 (w) of the horse naturally succeeds its fore- 

 arm, but from the fact of the upper arm 

 being concealed beneath the skin and 

 muscles, the wrist is not usually recognised 

 as such. Thus, when a horse chips its 

 "knee," it, in reality, suffers a contusion of its 

 wrist. Man possesses eight bones in his 

 wrist; the horse has only seven, but the 

 equine wrist is readily recognisable as cor- 

 responding with the similar region in man. 

 The greatest difference between the human 

 limb and that of the horse is found in the 

 regions which succeed the wrist, and which 

 constitute the palm and hand. Man has 

 five palm-bones : the horse has apparently 

 but one long bone, the "cannon bone" (a* 1 ^ 

 in place of the five. Now, to which of man's 

 palm-bones does this " cannon bone " corre- 

 spond ? The anatomist replies, " To that 

 supporting the third or middle finger ; " and 

 attached to this single great palm-bone the 

 horse has three joints or " phalanges " (i, 2, 3) 

 composing his third finger. These joints are 

 well known in ordinary life as the " pastern," 

 " coronary," and " coffin bones : " and the 

 last bears the greatly developed nail we call 

 the " hoof." 



Thus the horse walks upon a single finger 

 or digit the third ; and it behoves us to ask what has become of 

 the remaining four five being the highest number of fingers and toes 

 found in mammals or quadrupeds. We find that, with the exception 

 of other two the second and fourth fingers the horse's digits 

 have completely disappeared. The second and fourth fingers have 

 left mere traces, it is true, but it is exactly these rudimentary 

 fingers which serve as the chief clues to the whole history of the 

 equine race. On each side of the single palm-bone (m l ) of the 

 horse's great finger we see two thin strips of bone (one of which is 



FIG. 32. 

 BONES OF HORSE'S FORE-LIMB. 



