CLEWS IN NATURAL HISTORY. 23 



whales of to-day a creature this, of which, as regards its teeth at least, 

 modern whales are but shadowy reproductions. While under the shel- 

 ter of great authority we may declare this ancestor of the whale to have 

 been intermediate in nature between the seals and whales, or between 

 the whales and their neighbors the manatees or sea-cows and dugongs. 

 In either case, the intermediate character of the animal argues in favor 

 of its having been the likely parent of a race dentally degraded in these 

 latter days. 



There is little need to specialize further instances of the occurrence 

 of rudimentary organs in the higher animals, save to remark that not 

 the least interesting feature of such cases is contained in the fact that 

 the milk-glands of male animals among quadrupeds organs which exist 

 in a rudimentary condition have been known to become functionally 

 active and to secrete milk ; this peculiarity having been known to occur 

 even in the human subject. Among the higher quadrupeds, however, 

 there yet remains for extended notice one special instance of the occur- 

 rence of " rudimentary organs," wherein, not merely is the nature of 

 the parts thoroughly determined, but the stages of their degradation 

 can be clearly traced through the remarkable and fortunate discovery 

 of the " missing links." Moreover, the case in point, that of the horse, 

 so clearly illustrates what is meant by progressive development or evo- 

 lution of a species of animals, that it is highly instructive, even if re- 

 garded from the latter point of view. 



When we look at the skeleton of a horse's fore-limb, 

 we are able, without much or any previous acquaintance 

 with the facts of comparative anatomy, to see that it is 

 modeled upon a type similar to that of the arm of man. 

 Were we further to compare the wing of the bird, the 

 paddle of the whale, the fore-limb of the bat, and the fore- 

 leg of a lizard, with the equine limb, we should find the 

 same fundamental type of structure to be represented in 

 all. Thus we find in the arm of man (Fig. 8) to select 

 the most familiar example from the series just mentioned 

 a single bone, the humerus ( 3 ), forming the upper arm ; 

 two bones {radius ( 4 ) and ulna ( B ) ) constituting the fore- 

 arm ; eight small bones forming the wrist {carjms) : five 

 bones one for each finger forming the palm or meta- 

 carpus and five fingers, each composed of three small bones, named 

 phalanges, with the exception of the thumb, in which, by a mere in- 

 spection of that digit, we may satisfy ourselves only two joints exist. 

 In the wing of the bird (Fig. 9) we find similarly an upper-arm bone or 

 humerus, two bones {radius and uhia) in the forearm ; a wrist {b), a 

 thumb {g), and two fingers {cfe d). Now, turning to the fore-limb of 

 a horse (Fig. 10) the hind-limb being essentially similar, in its gen- 

 eral conformation, and corresponding as closely with man's lower limb 

 we find its conformation to correspond in a remarkable fashion to that 



