Ill LECTUftES ON EVOLUTION 117 



end of the ulna. This is closely united with the 

 chief mass of the bone which represents the radius, 

 and runs out into a slender shaft which may be 

 traced for some distance downwards upon the back 

 of the radius, and then in most cases thins out and 

 vanishes. It takes still more trouble to make sure 

 of what is nevertheless the fact, that a small part 

 of the lower end of the bone of the horse's fore- 

 arm, which is only distinct in a very young foal, 

 is really the lower extremity of the ulna. 



What is commonly called the knee of a horse 

 is its wrist. The " cannon bone " answers to the 

 middle bone of the five metacarpal bones, which 

 support the palm of the hand in ourselves. The 

 "pastern," " coronary," and u coffin" bones of vet- 

 erinarians answer to the joints of our middle 

 fingers, while the hoof is simply a greatly enlarged 

 and thickened nail. But if what lies below the 

 horse's "knee" thus corresponds to the middle 

 finger in ourselves, what has become of the four 

 other fingers or digits ? We find in the places of 

 the second and fourth digits only two slender 

 splint-like bones, about two-thirds as long as the 

 cannon bone, which gradually taper to their lower 

 ends and bear no finger joints, or, as they are 

 termed, phalanges. Sometimes, small bony or 

 gristly nodules are to be found at the bases of 

 these two metacarpal splints, and it is probable 

 that these represent rudiments of the first and fifth 

 toes. Thus, the part of the horse's skeleton, which 



