NO.. 6 EAR EXOSTOSES HRDLICKA 53 



majority of cases reported only those areas responded to this stimulation, what- 

 ever it was, which during the development grew most rapidly. These places are 

 the two ends of the annulus. By far the larger number of aural exostoses are 

 found along the suture lines between the canal and the rest of the temporal bone. 

 Why? The author believes that an adequate explanation is to be found in his 

 theory that these susceptible areas have retained their early potentiality of 

 more rapid development and response to any stimulus of production. 



For Alexander (1930) the "deeper causes of ear exostoses He in 

 the temporal bone, which is formed of parts that ossify in cartilage 

 and parts formed from periosteal ossification ; also the persistence of 

 cartilaginous points in the petrosum, and the lateness of the close 

 of the postembryonal growth, create a disposition to variation in the 

 bone and pathological growths." 



Critical remarks. — Although the theory of a " developmental " 

 origin of some, at least, of the ear exostoses has received a considerable 

 backing, yet most of this appears of the order of " follow the leader ". 

 And neither the leader nor those who followed have furnished the 

 slightest material evidence that would bear out their contention, or 

 even make it possible. 



The discussion under " Congenital Origin " applies also here. There 

 a:-e no observations on record of a fetal, or even later, involvement by 

 the growths up to Field's child of 3 years, and even that case is 

 unique. The bony parts that are to form the external meatus and 

 from which eventually exostoses may arise, are still largely deficient 

 in fetal life and are still far from complete at birth. And irritative 

 ear troubles, that could excite the formation of the outgrowths, are 

 not known of before birth. 



INBORN TENDENCY 



Wholly different from congenitality is the case of the causes com- 

 prised under the term " inborn tendency ". Here is something worthy 

 of earnest attention. 



The suggestion that there may be behind ear exostoses an inborn 

 tendency toward their production has been expressed by a number of 

 writers on the subject, though one would vainly search for any com- 

 prehensive exposition of the idea. Thus Nelaton speaks of a " predis- 

 position generale de I'economie ", and Delstanche (1878), who quotes 

 him, admits this as among the causes. Masini (1882) names " immi- 

 nent predisposition", and Ostmann (1894) mentions "inborn ten- 

 dency" as among the causes of the exostoses. For Russell (1900) 

 there is a " tendency in all races towards the formation of bony tumors 



