XVII] THE COMPARISON OF RELATED FORMS 



•69 



(P), that the configuration of the angle of the jaw does not tally 

 quite so accurately with that of our hypothetical diagrams as do 

 other parts of the skull. As a matter of fact, this region is 

 somewhat variable, in different species of a genus, and even in 

 different individuals of the same species ; in the small figure {Pp) 

 of Protohippus placidus the correspondence is more exact. 



In considering this series of figures we cannot but be struck, 

 not only with the regularity of the succession of " transformations," 

 but also with the slight and inconsiderable differences which 

 separate the known and recorded stages, and even the two extremes 

 of the whole series. These differences are no greater (save in 

 regard to actual magnitude) than those between one human skull 

 and another, at least if we take into account the older or remoter 



Fig. 403. Human scapulae (after Dwight), A, Caucasian; B, Negro; 

 C, North American Indian (from Kentucky Mountains). 



races; and they are again no greater, but if anything less, than 

 the range of variation, racial and individual, in certain other 

 human bones, for instance the scapula*. 



The variabiHty of this latter bone is great, but it is neither 



what few gaps remain. So closely do successive stages follow upon one another 

 that it is sometimes extremely difficult to arrange them all in order, and to 

 distinguish clearly those members which belong in the main line of descent, and 

 those which represent incipient branches. Some phylogenies actually suffer from 

 an embarrassment of riches." 



* Cf. Dwight, T., The Range of Variation of the Human Scapula, Amer. Nat. 

 XXI, pp. 627-638, 1887. Cf. also Turner, CMllenger Rep. XLvn, on Human Skele- 

 tons, p. 86, 1886: "I gather both from my own measurements, and those of other 

 observers, that the range of variation in the relative length and breadth of the 

 scapula is very considerable in the same race, so that it needs a large number of 

 bones to enable one to obtain an accurate idea of the mean of the race." 



T G. 49- 



