384 



fitness of the method by which their interrogation of nature was 

 conducted. 



I apprehend that it has been and is, too often forgotten that 

 the phrase "Theory of the Skull " is ordinarily employed to denote 

 the answers to two very different questions ; the first, Are all verte- 

 brate skulls constructed upon one and the same plan ? the second, 

 Is such plan, supposing it to exist, identical with that of the verte- 

 bral column? 



It is also forgotten that, to a certain extent, these are inde- 

 pendent questions ; for though an affirmative answer to the latter 

 implies the like reply to the former, the converse proposition by no 

 means holds good ; an affirmative response to the first question being 

 perfectly consistent with a negative to the second*. 



As there are two problems, so there are two methods of obtaining 

 their solution. Employing the one, the observer compares together 

 a long series of the skulls and vertebral columns of adult Fertebrata, 

 determining, in this way, the corresponding parts of those which are 

 most widely dissimilar, by the interpolation of transitional gradations 

 of structure. Using the other method, the investigator traces back 

 skull and vertebral column to their earliest embryonic states, and 

 determines the identity of parts by their developmental relations. 



It were unwise to exalt either of these methods at the expense of 

 its fellow, or to be other than thankful that more roads than one 

 lead us to the attainment of truth. Each, it must be borne in mind, 

 has its especial value and its particular applicability, though at the 

 same time it should not be forgotten, that to one, and to one only, 

 can the ultimate appeal be made, in the discussion of morphological 

 \ questions. For seeing that living organisms not only are, but become, 

 and that all their parts pass through a series of states before they 

 reach their adult condition, it necessarily follows that it is impossible 

 to say, that two parts are homologous or have the same morphological 



* There is a wide difference, too, in the relative importance of either question 

 to the student of comparative anatomy. Unless it can be shown that a general 

 identity of construction pervades the multiform varieties of vertebrate skulls, a 

 concise, uniform, and consistent nomenclature becomes an impossibility, and the 

 anatomist loses at one blow the most important of aids to memory, and the most 

 influential of stimulants to research. The second question, on the other hand, 

 though highly interesting, might be settled either one way or the other, without 

 exerting any very important influence on the practice of comparative anatomy. 



