NO. 6 EAR EXOSTOSES HRDLICKA 39 



nesian groups, in the two Dakotas and in the northeastern American 

 States, there were no exostoses that could be recorded as " large ". 

 In the Egyptians, the Pueblos, and the Hawaiians, in particular, not- 

 withstanding their widely differing total involvement by the growths, 

 the exostoses were all or almost all small. The greatest collective 

 " massiness " of the abnormal formations occurred in Kentucky, 

 Virginia, Arkansas, Florida, and Peru — again under widely differing 

 total involvement. 



The causes of the above differences are not clear. If it were prac- 

 ticable to divide the basic causes of these exostoses into hereditary 

 and those checking, or again favoring or exciting, their development 

 and growth in the predisposed individual — as may be correct — ^then 

 it could be conceived that the differences in their total bulk in a group 

 were due proportionately to the checking or favoring factors. Another 

 influence that enters into the subject is that of age. The growths 

 need time for their development to a large size. Of two groups equally 

 subject to the exostoses the younger would presumably show less 

 mass of the growths. It is probable that the mean age of the affected 

 skulls is not the same in all the groups. But age alone could not 

 possibly account for all the differences encountered. 



One item is clear from the results shown in the preceding table, 

 and that is that the numerical involvement by ear exostoses in differ- 

 ent groups does not always go hand in hand with the collective massi- 

 ness of the growths. 



SHAPES 



Ear exostoses occur in many shapes, and these merge with each 

 other so much that any definite classification appears impossible. Blake 

 (1880) believed that he could recognize two main forms, the 

 " rounded " and the " flattened ". Von Troeltsch (1881) divided the 

 better differentiated ones into broad-based and pedunculated. Kessel 

 (1889, p. 285) states they are " multiform ", but fall into three classes, 

 namely, Ijyperostoses, periostoses, and exostoses ; under the latter 

 " are understood more or less circumscribed tumors that grow espe- 

 cially in one direction and stand either vertically to or parallel with 

 the axis of the canal. One can observe rounded, cylindrical, and 

 conical exostoses " — but there are also transitional and peculiar forms ; 

 there are, too, spinelike growths which have been called " osteo- 

 phytes ". For Schlomka (1891, p. 16), who doubtless in part follows 

 Kessel, " one can speak of rounded, cylindrical, or conical exostoses ; 

 but there are many combinations of these forms ", and some of the 

 growths may assume the form of ossified polyps. Sabroux (1901, 



