NO. 6 EAR EXOSTOSES HRDLICKA 3I 



The data on page 30 show the following conditions : 



1. In general, in a group the larger the number of individuals af- 

 fected by ear exostoses, the more commonly both ears are involved. 



2. The frequency of bilateral as compared to unilateral involvement 

 varies from 33 to 79 percent in the different series of our material. 



3. When but one side is involved, there is a perceptibly greater 

 tendency for the abnormalities to develop in the left ear. In the 

 [4 groups of our crania, in 9 the involvement was more frequent on 

 the left side, in 3 on the right side, and in 2 groups it was equal on 

 the two sides. 



The proportions of bilateral involvement in our series agree fairly 

 closely with those of Bezold (54.4 percent) and Korner (64 percent) 

 on European Whites. Through all this the affliction again impresses 

 one as something of a pathological entity. 



As it is probable that some proportion, at least, of the individuals 

 whose skulls enter into these series, if they had lived longer, would 

 have developed the condition bilaterally, it may be assumed that the 

 general tendency for the tympanic exostoses is to involve both auditory 

 canals ; but they evidently tend to start more frequently on the left 

 side. Why this should be so is not apparent, but it is probably con- 

 nected with nervous and vascular factors. 



The very apparent tendency toward a bilateral involvement should 

 be an important factor in the study of the deeper causes of these 

 formations. 



NUMBER 



Ear exostoses may be single or multiple." Delstanche (1878) en- 

 countered up to three in one ear. Von Troeltsch saw " frequently 

 several in one ear, arising from different parts of the wall." Sabroux 

 (1901, p. 35), from the data he gathered, believed them to be " ordi- 

 narily single ", though there might be two or even three in one ear. 

 For Kerrison (1913, p. 125) they were " multiple oftener than single." 



Blake (1880) and Korner (1894, p. 107) alone give some statistics 

 on the point. In Blake's 39 cases of ear exostoses in Tennessee and 

 California Indians, 54 of the 78 ears showed the growths : in 38 ears 

 (70.4 percent) they were single, in 12 (22.2 percent) double, in 3 

 (5.6 percent) triple, and in i (1.8 percent) multiple. In 41 ears 

 Korner found the exostoses 32 times (78 percent) single, 8 times 

 (19.5 percent) double and once (2.7 percent) triple. The two records 

 are remarkably harmonious. 



Aside from Blake's there are no data on this subject in the published 

 reports of a more anthropological nature. Among the clinical records 



