86 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 



Ear exostoses are localized hyperplasias, or outgrowths, from es- 

 sentially the tympanic part, but occasionally also from the squamous 

 portion, of the external bony meatus. 



They arise generally from what were the free upper ends of the 

 tympanic ring. Their development belongs chiefly to the later adoles- 

 cent period and the earlier half of the adult period. 



A " predisposition " to ear exostoses is now probably universal in 

 man, but in some races or groups the formation of the abnormalities, 

 owing perhaps to direct hereditary effects, is much more frequent than 

 in others. 



Males are considerably more subject to the growths than females, 

 the well-to-do (in Whites at least) more than the poor. The affection 

 is most frequently bilateral, and where one-sided, it occurs somewhat 

 more commonly in the left than in the right ear. 



Structurally, the growths range from cancellous to compact, with- 

 out any definite segregation. Though macroscopically the bone is 

 often more or less aberrant, its elements are normal and remain 

 viable. There is never any breaking down or necrosis, nor a com- 

 plete calcification. 



The causes are systemic or " predisposing ", and exciting. The 

 paramount systemic cause appears to be a deranged neuro-vascular 

 control of the parts involved, chiefly the tympanic bone, during what 

 corresponds to the sexually more active part of life ; but on critical 

 consideration it becomes apparent that no connection of the exostoses 

 with sex activity can be ascertained. 



What causes the peculiar time-limited neuro-vascular derangement 

 that predisposes or leads to ear exostoses cannot yet be definitely es- 

 tablished, but it appears to be something in the hereditary endowment 

 of the trophic nervous centers that control the normal status of the ex- 

 ternal bony meatus. A deranged accommodation of evolutionary na- 

 ture suggests itself, rather than degeneracy, as a plausible explanation. 



The exciting cause of ear exostoses, where the predisposition to 

 these exists, may be anything mechanical or chemical that produces 

 prolonged irritation, with consequent hyperaemia to inflammation, 

 of any part of the bony meatus. 



BIBLIOGRAPHY 



AlCHEL, O. 



1931. Diskussionsbemerkung zu Moller-Holst : Uber Gehorgangsexostosen 

 Lisw. Sitzungsber. Ges. Phys. Anthrop., Breslau. 

 Alderton, H. a. 



1898. Some unusual aural cases. Ann. Otol. Rhin. and Laryng., vol. 7, 

 no. I, pp. 115-118. 



