no. 1641. AMERICAN INDIAN SKULLS— HRDLIl'h I. 175 



The ultimate causes of each of the above defined categories of cases 

 are not as yet clearly established. They are in all probability some- 

 times biological and sometimes pathological in nature, (he first com- 

 prising reversions of form, subaverage development of the brain or 

 the frontal lobes, and rarely, perhaps, a great development of the 

 temporal muscles, while the latter ma} 7 conceivably include patho- 

 logical expansion of the frontal sinuses, a hyperplasia of the antero- 

 inferior portions of the frontal bone, pathological defects of the 

 frontal lobes, and such conditions of the frontal squama as would 

 result in an abnormal resistance of the bone to the forward expansion 

 of the growing brain. Regarding the last item, it must be borne in 

 mind that the brain expands in the direction of least resistance, a 

 fact amply demonstrated in the study of pathological as well as 

 artificial deformations of the skulls and any increase in the normal 

 resistance of the forehead part of the frontal bone before the growth 

 of the brain has been completed — an increase such as may follow a 

 premature closure of the metopic articulation — is bound to be fol- 

 lowed by a less perfect development of the frontal convexity. 



In the anthropoid apes and some of the lower old-world primates the exten- 

 sive attachment and development of the temporal muscles has a marked effect 

 on the formation and dimensions of the distal portion of the supraorbital crest. 

 The orang shows this to the best advantage. It may be worthy of remark in 

 this place that the skull of Dubois's pithecanthropus is much more related in 

 this respect to the orang than to any of the other living anthropoids. 



6 See in this connection writings on deformed skulls, an extensive bibliog- 

 raphy of which can be found in the Catalogue of the Surgeon-General's Library, 

 U. S. A., and particularly II. Virchow's " Ueber den Cretinismus, namentlich in 

 Franken, und uber pathologische Schadelformen " ; Ges. Abh. z. wiss. Medicin, 

 Svo, Frankfurt a. M., 1S56, p. S91 et seq. 



