THE MUSCLES OF THE LOWER EXTREMITY 189 



" This eminent anatomist applied these myological for- 

 mulae to a classification of the entire group of existing 

 birds, and fully discussed the matter in his work in the 

 most masterly manner in so doing, but it will be im- 

 possible to enter upon any such field here. In my own 

 opinion, however, I am. inclined to believe that Garrod's 

 classification stands in need of a very thorough overhaul- 

 ing in many of its aspects ; by this I mean that in a vast 

 number of cases we are not in possession of the requisite 

 knowledge of the entire structure of certain forms as to 

 warrant one retaining them where Garrod has placed 

 them. In other words, these myological formulae, as 

 time goes by, and our knowledge of avian morphology 

 widens, will surely prove very useful in taxonomy, but 

 they can only be employed with safety when taken, as 

 one set of characters, in connection with all the others 

 that the organization of any particular bird-form pre- 

 sents us with, and by no means are we to rely upon 

 them alone, or even when a few other sets of structural 

 characters seem to indicate a bird's affinity. 



" To illustrate my point, let us turn for a moment to 

 the Swifts and Humming-birds ; here we have two 

 groups which for years past have been associated to- 

 gether as allied forms by systematists, and Garrod, too, 

 seemed to believe in their affinity. Why ? Because 

 the formula for the thio;h-niuscles in each case was 



O 



found to be A ; the sternum had in each case an un- 

 notched posterior border ; and neither Swifts nor Hum- 

 mers possess intestinal caeca. Yes, this all may be so, 

 but all the rest of the organization of these birds is as 

 widely different as one can well imagine, and conse- 

 quently they belong to very different orders of birds. 

 This latter statement gains weight when we come to 

 think that aside from the formula for the thigh-muscles 



