1871.] 313 [Wilder. 



Now since these five relations above described, however they may 

 differ among ifheniselves as to the particular regions of two parts 

 which are compared together, are all relations of homology, it may 

 probably be taken for granted that whatever criteria are accepted for 

 one kind of homology, are equally applicable to the rest; excepting, 

 of course, the tropical relations which depend upon the position of 

 the parts with reference to the axis of the body. If this is granted, 

 then, we are entitled to employ the arguments used in deciding any 

 one of the relations upon which there is now no dispute, in determin- 

 ing those now under consideration. 



For instance, the tertius of a seal is determined to be the plural 

 homologue of the middle dactyl of a rhinoceros, not from its size 

 or function, but from its relative position in the pes; the tertius of 

 man is held to be the meketrope of the medius, from their similar rel- 

 ative position, although the one is a short dactyle, and the other is 

 the longest digit; again, the primus of man is held to be homolo- 

 gous with the primus of a bat, although they differ not only in size 

 and function, but in their apparent relative position, since the human 

 primus is on the inner border of the pes, and that of the bat becomes 

 the " outer toe " through the complete eversion of the skelos; we here 

 see that relative normal position is of superior morphical value to 

 size, function, and natural attitude; finally, the homology between 

 the human primus and that of an orang has never been questioned, 

 although the latter often, if not generally, consists of but a single 

 phalanx; the homology between the minimus of an ordinary mammal 

 and that of a bat has never been denied, although the latter rarely, 

 if ever, consists of the usual number of phalanges ; no one has even 

 doubted the entire homology of the five digits of many tortoises, (Ow., 

 63, 1, p. 173) with those of the Mammalia, as is shown by the use of 

 the same names (pollex, etc.,) yet none of the former have more than 

 two phalanges; a like discrepancy exists with the birds; and, if, as I 

 am willing to admit, it is better to confine the comparisons to the 

 Mammalia, an even more striking case is offered by many Cetacea, 

 where the digits are enumerated from one to five, (or styled pollex, 

 etc.,) and where the subdivisions of the digits are invariably called 

 phalanges, although in some cases, as in the round-headed dolphin, 

 (Globiocephalus wielas), the medius may possess eight and the index 

 twelve of them, and although the form, function, and attitude of the 

 entire manus be unlike that of man. 



It appears therefore, that in the determination of all kinds of ho- 



