NO. 6 EAR EXOSTOSES HRDLICKA 73 



pression of the back of the head with similar etfects on the ear occurs 

 in some of the cases of the simple occipital flattening, without resulting 

 in tympanic exostoses. 



It seems that it is the forcible frontal compression which is mainly 

 to blame. The stresses within the skull produced by the fronto- 

 occipital forcing are certainly greater than those in simple occipital 

 compression. The shape of the external auditory canal is certainly 

 affected in many of these cases. But just how this could give rise to 

 the exostoses is not clear, especially as such growths do not appear to 

 develop earlier in the flat-heads than they do in other crania. Much 

 evidently remains to be learned in these connections. 



The simple fact that definitely emerges from our data is that the 

 fronto-occipital head deformation in the newborn of a group is as 

 a rule attended with an increased frequency of development of ear 

 exostoses later in life in that group. The size, forms, and locations 

 of the growths remain apparently unaffected. As to the cause f (jr the 

 increase in frequency, it could be conceived that where artificial head 

 flattening was practiced for a long period of time and favored the 

 development of ear exostoses, the tendency toward these became 

 more and more " alive ", and perhaps also the abnormalities became 

 multiplied through direct heredity in families, thus increasing their 

 frequency in the group, even in the undeformed heads. There is 

 probably a kernel of truth in this, though for the present the idea 

 must remain in the category of speculation. 



MISCELLANEOUS CAUSES 



As in other cases where the causation of a condition is obscure, 

 so with ear exostoses, the students of the subject in the course of 

 time have advanced about the whole gamut of theories that could well 

 be made in this connection. Aside from those dealt with in the previ- 

 ous pages may be mentioned the following : 



INBRKEDING 



Moller-Holst (1932) believes that the pathological ear exostoses, 

 as well as the normal thickening of the tympanic bone such as found 

 in the Eskimo, have arisen through inbreeding (see p. 56). 



CONSTITUTIONAL DISEASES (OTHER THAN SYPHILIS AND ARTHRITIS) 



Heiman ( 1890) regarded scrofula as favoring a development of ear 

 exostoses, but only indirectly, through its favoring inflammatory con- 

 ditions in the auditory canal. There are a few other weak references 



