IN THE LIMBS OF MAMMALIA. 21 



tions between the fore and hind limbs, but as will be seen, they are only apparent, and 

 against their entertainment may be urged all that has been, and much more that might be, 

 said concerning the distinctions between morphology and teleology, and the fallacy of 

 deductions from either respecting the other. 



The first is, that by rotating back so as to leave the ulna and the radius parallel, 

 the former must correspond to the inner bone of the leg, tibia., and the latter to the outer 

 bone, fibula ; yet the radius forms most of the wrist joint, and the tibia forms the ankle, and, 

 as the power of rotation gradually disappears in the mammalian series, it is the ulna in the 

 fore leg, and the fibula in the hind leg, which decreases in size through the carnivora, till in 

 the permanently pronated fore-arm of the ruminants, solipeds, and some pachyderms, the 

 ulna is represented only by the olecranon process and the upper half of the shaft soldered 

 to the radius, while in the posterior limb scarce a trace of the fibula remains ; in other 

 words, the homologous bones of the two extremities are developed in an inverse instead of 

 a direct ratio ; but relations of more and less, like those of form, are always dependent upon 

 function, and therefore not safe guides to homology, so that this cannot be taken as a real 

 objection to the law of longitudinality, borne out as it is by the entire vertebrate structure 

 wherever the original plan is retained or can be detected under its various teleological 

 modifications. We may however connect this fact with another, so that it shall to us seem 

 to have, what with all things in nature it certainly must have, a more or less remote foun- 

 dation in use. As we have seen above, in a morphological point of view, the ulna is the 

 inner, and the radius the outer, bone. This is the relation which they bear in the fcetus 

 and which harmonizes best with other parts ; but this admits of such variation that in nearly 

 all mammals below the quadrumana, the radius becomes inner and the ulna outer. Now, 

 for some cause not yet understood, it is best for both hand and foot in quadrupeds to be 

 connected with the inner bone of the legs, and in provision for this the hand is in all the 

 mammalia supported by the radius which in the four-footed members of the class is the 

 inner bone. 



The second and more obvious though equally fallacious objection is, that of the five 

 digits which terminate the anterior and posterior extremities, the outer ones will then be 

 the thumb and the little toe, and the inner ones the little finger and great toe. Perhaps 

 no correspondence has been more generally admitted, and even taken as a basis for other 

 investigations, than the analogy between the thumb and the great toe, not only because 

 in the commonly accepted condition of the parts they both occur on the inner sides of the 

 hand and foot, but because they are so constantly composed of two phalanges, while all the 

 other digits possess three. 



But even if it were true, which it is not, that this same numerical relation prevailed 

 among the three other classes of the vertebrate sub-kingdom, and there were therefore some 

 grounds for regarding as morphological a rule for which no sufficient teleological cause is 

 yet apparent, we could not reasonably accord to any deviation at the very distal extremi- 

 ties of the limbs, a value sufficient to outweigh the teachings of all parts between them and 

 the morphological centre of the body; and it is better to acknowledge our ignorance of the 

 meaning of one fact than to purposely ignore the existence of others far more numerous 

 and important. 



I will here mention the comparisons between the anterior and posterior extremities of 

 vertebrates which, since the time of Winslow, (1775,) have been made by many of the most 



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