1866.] 5 [Wilder. 



vertebras, and then, In looking for its homologue in the cat, to com- 

 mence at the tip of the tail and, not finding the fifth therefrom to be 

 such a bone, to deny the existence of a sacrum in that species ; or if 

 this is an exaggeration, to compare two human spines, in one of which 

 were four and the other five coccygeal vertebra), and to conclude 

 that in the latter was a misplacement of the sacrum rather than an 

 unusual number of coccygeal elements : this, I say, would be as reas- 

 onable as to attempt to determine morphological relations by refer- 

 ence primarily to parts so far from the morphological centre, so sub- 

 ject to teleological modifications, and so liable to variation from vege- 

 tative repetition, as are the terminal segments of the limbs. 



And yet almost invariably, not only in popular but in scientific 

 comparisons between the fore and hind limbs of vertebrates, there is 

 assumed at the outset a parallelism between them and a correspond- 

 ence of the thumb with the great toe, and of the little finger with 

 the little to^ : no doubt these do correspond with each other, but this 

 by analogy, not homology ; the resemblance is teleological, not mor- 

 phological, and depends upon external form and function as pre- 

 sented in the mammalia, rather than upon essential structure and 

 the relations which they hold to other portions of the limbs, and to 

 their homologues among the three lower classes of vertebrates : for 

 though in mammalia the two digits which in men bear the names of 

 thumb and great toe consist of only two phalanges, while all the 

 others po'ssess three, yet no such numerical relation exists among 

 the birds, the reptiles and the fishes. 



The philosophical method is that adopted by Professor Jeffries 

 Wyman.* To begin our comparison by reference first to the 

 proximal segments of the limbs, or still better, back to the main 

 axis and to the outlets of the internal organs, which would sug- 

 gest that between the two ends of the body is a certain oppositeness 

 or antagonism or polarity, both morphological and teleological, similar 

 to, though less obvious than, that which is so universally recognized 

 between the right and left sides ; and now in approaching the limbs 

 we should find that " corresponding segments point and are flexed or 

 extended in absolutely opposite though relatively similar directions. "f 

 At least this is the case till we reach the hands, and then, the forearm 

 being in a state of supination, the ulna and radius are parallel and 

 are seen to correspond with the tibia and fibula respectively : while 

 the palm points downwards and forwards and the sole of the foot 

 downwards and backwards. Having recognized all this we shall be 



* On anterior and posterior symmetry in the limbs of Mammalia. Proceedings 

 Bost. Soc. ^'at. Hist., June 6th, 1860. 



t See my Memoir on Morphology and Teleology, page 20, in Memoirs Bost. Soc. 

 cf Nat. liist., Vol. I., Tart 1. 



