148 OEGANS OF LOCOMOTION 



regulating the length ; whilst the multiplied movements of the 

 thumb and fingers perform the special acts which the hand was 

 designed so admirably to execute. The quadrumana, like man, 

 have the thumb opposable to the other fingers. It is this, in fact, 

 which forms the true character of the hand. But the bones of 

 the thumb in man are more lengthened and powerful, in propor- 

 tion to the other fingers, than in monkeys, whose hand does 

 not equal his in perfection ; for monkeys can neither seize 

 minute objects with that precision, nor grasp and support large 

 ones with that firmness which is so essential to the dextrous 

 performance of the multitudinous purposes for which the hand 

 of man was designed. T. W.] 



1. PLAN OF THE ORGANS OF LOCOMOTION. 



279. The organs of progression in vertebrated animals 

 never exceed four in number, and to them the term limbs is 

 more particularly applied. The study of these organs, as 

 characteristic of the different groups of vertebrate animals, is 

 most interesting, especially when prosecuted with a view to 

 trace them all back to one fundamental plan, and to observe 

 the modifications, oftentimes very slight, by which a very sim- 

 ple organ is adapted to every variety of movement. No part 

 of the animal structure more fully illustrates the unity of de- 

 sign, or the skill of the Intellect, which has so adapted a single 

 organ to such multiplied ends. On this account we shall 

 illustrate the subject somewhat in detail. 



280. It is easy to see, that the wing which is to sustain 

 the bird in the air (fig. 1 64), must be different from the leg of 

 the stag (fig. 160), which is to serve for running, or the fin of 

 the fish (fig. 168) that swims. But, notwithstanding their dis- 

 similarity, the wing of the bird, the leg of the stag, and the 

 shoulder fin of the fish, may still be traced to the same plan of 

 structure ; and if we examine their skeletons, we find the same 

 fundamental parts. 



281. In the arrn of man (fig. 78), the shoulder-blade is 

 flat and triangular ; the bone of the arm is cylindrical, and 

 enlarged at its extremities ; the bones of the fore-arm are 

 nearly the same length as the humerus, but more slender ; the 

 hand is composed of the eight small bones of the carpus, 

 arranged in two rows, five metacarpal bones, which are elon- 

 gated, and succeed those of the wrist ; five fingers of unequal 

 length, one of which, the thumb, is opposed to the four others. 



