54 Dynamic Theory. 



ment have become so persistent, and, second, indicate the manner in 

 which the short cuts of nature's work are accomplished. Two move- 

 ments or processes follow each other, at first slowty, then, as facility is 

 acquired, more rapidly and more rapidly till the two become simul- 

 taneous, blend into one, and become a compound process as two 

 sounds may be repeated alternately yet so rapidly as to be confounded 

 as one to the human sense, and two colors the same ; so in development, 

 two or a dozen steps may be taken in such rapid succession as to evade 

 human sense, or still more rapidly so that the two or dozen are only*one. 

 It is undoubtedly true that five digits is the normal number for the 

 vertebrates, from the amphibians up to man, but in the great majority 

 an exception is made by the loss of one or more digits on either the fore 

 or hind limb. 



FIG. 68. Bones of fore limb of an amphibian (frog &c). 

 h. Upper arm, humerus. 

 r u. Radius and ulna of the forearm. 

 r' u' ceil 23 4 5. Boot bones of the hand, 

 r'. Radial. 

 u'. Ulnary. 

 . Intermediate. 



FIG. 69. Skeleton of right fore foot or hand of I man, II dog, 

 III pig, IV ox, V tapir, VI horse. 



r. Radius ) ^ 



u ulna } -oones of fore-arm. 



a. Scaphoid. ) ** 

 b. Semi lunar J - 

 c. Cuneiform ^ 

 d. Trapezium l>* 

 p-Tvapezoid. f 



l.-Tlmmh. 

 2. Index. 

 3. Middle finger, 

 4. Ring finger. 

 6. Little finger. 



/.Magnum. 



ff Unciform. |. 



p. Pisiform. J & 



The horse has lost all his digits except the middle finger, on 

 which he walks. The ox has two, the pig two useful and two rudi- 

 mentary ones. (After Gegenbauer.) 



FIG. 68. 



FIG. 69. 



Originally the five-toed animal was a plantigrade, the entire hand or 

 foot being placed on the ground in walking. But in the struggle for 



