EVIDENCE FROM TAILS, LIMBS, & LUNGS OF ANIMALS. 109 



structure which is literally amazing. A very slight examination of the 

 limbs of a horse would convince us that, roughly regarded, the parts 

 or segments of the fore-limb (Fig. 32) correspond to those of the hind- 

 limb (Fig. 33). There usually exists a degree of correspondence between 

 fore- and hind-limbs which is easily observed, but which, on the other 

 hand, in such animals as bats and birds appears less easy of detec- 

 tion. But, laying aside external appearances as thoroughly unreliable, 

 let us appeal once again to comparative anatomy, and inquire, firstly, 

 into the likenesses and differences between limbs ; and secondly, into 

 the nature and manner of origin of these important appendages. 



In the arm of man (Fig. 47, A) we find an upper arm bone (#), 

 two bones in the fore-arm (b and <r), eight bones in the wrist (d\ five 

 in the palm (e) of the hand, and three in each of the fingers (/), 

 save the thumb, which is composed of but two bones. Thus it 

 would seem that in the arm of man there are some three chief seg- 

 ments, namely, upper arm, fore-arm, and hand ; and in the lower 

 limb the same elementary divisions, corresponding to thigh, leg, and 

 foot, may be discerned. Man has five fingers, which, reckoning from 

 the thumb side, we may number one, two, three, four, and five respect- 

 ively ; the great toe being similarly the first digit of the foot. In 

 the wing or arm of the bat (F) a type of structure exactly similar to 

 that seen in man's arm is readily perceived. The upper arm (a\ 

 fore-arm (b c\ (with one of its bones [c] somewhat degraded in size,) 

 the wrist (d), the palm (e\ and the fingers (/), are fully represented 

 in the bat ; but the four fingers are greatly elongated to support the 

 fold of skin forming the flying-membrane, and the thumb (g) is of 

 small size. No doubt can exist, therefore, that the arm or fore-limb of 

 man is exactly similar to that in structure, or, in other words, is 

 " homologous " with the arm or fore-limb of the bat. In the paddle 

 of the whale (D), shortened and modified as that limb may be, w r e 

 perceive a type of structure exactly corresponding with that of man 

 and the bat the upper arm (a), fore-arm (b c), wrist (d ), palm (e\ and 

 fingers (/), being readily seen when the skeleton of the paddle is 

 even cursorily examined. Of the wing of the bird (c), despite the 

 modification of its wrist and fingers, the same opinion in favour of 

 exact agreement with the human, bat, and whale type must be ex- 

 pressed. Upper arm (a) and fore-arm (b) are duly represented in 

 the wing ; and although but two wrist-bones (d\ two united (second 

 and third) fingers (<?,/), and a rudimentary thumb (g) exist, there 

 can be but one opinion as to the agreement of bird and man in 

 respect of the identity of their fore-limbs. In the horse (B), whilst 

 the limb itself, down to and including the wrist (d), exactly resembles 

 in all essential details the limbs already considered, (see preceding 

 chapter, page 90, et seq.) we find the fingers reduced to one the 

 third. Rudiments of the second and fourth fingers, however, also exist, 



