NO. 6 EAR EXOSTOSES HRDLICKA 35 



For M511er-Holst (1932, p. 96), who had the advantage of observ- 

 ing numerous cases in skulls, " the exostoses of the auditory canal 

 occur in the outer, middle, and inner portions of the canal. They are 

 located on the tympanic bone in different places, mostly on the boun- 

 dary of this bone and the squama or pars mastoidea. They seldom 

 proceed from the squama." In his material, " they occurred w^ith 

 about equal frequency anteriorly and posteriorly in the tympanic part ; 

 one-third of the cases showed them anteriorly, one-third posteriorly, 

 and the last third both anteriorly and posteriorly." 



Older records. — The only actual record on the location of ear ex- 

 ostoses within the meatus is that of Blake (1880). In 45 Indian skulls 

 with such growths, from Tennessee, California, and Arkansas, out of 

 a total of 82 exostoses 55 (66.3 percent) were posterior, 24 (28.9 

 percent) anterior, 3 (3.6 percent) antero-superior, and i (1.2 percent) 

 postero-inferior. 



New observations. — The location of the exostoses was noted in all 

 of our material. It was as shown in the table on page 36. 



Notwithstanding some significant differences, there is a remarkable 

 basic agreement in the figures, and also between that part of 

 them that embraces the bulk of the American Indian material and those 

 of Blake on the same race. 



It may now definitely be said that ear exostoses in the American 

 Indian (with a few exceptions), regardless of the amount of total 

 involvement by the growths, will be in something over 60 percent 

 (of all the exostoses) posterior, in from 20 to 40 percent anterior to 

 antero-superior, and in a small percentage — and that in but some of 

 the groups — postero-inferior or antero-inferior. Superior (squamous 

 part) outgrowths occurred in but three of the series, inferior out- 

 growths in but one and that only in a single instance. 



Some observers would perhaps be inclined to class some of the 

 cases included in " posterior " as postero-inferior or postero-superior, 

 but that would not alter the main significance of the above showing. 

 This is that, in general, in the American Indian, approximately two- 

 thirds of the ear exostoses arose from the posterior end or portion 

 of what was originally the tympanic ring and later developed into the 

 tympanic bone ; that nearly one-third of the growths arose from the 

 anterior end of the ring and subsequent bone ; and that in but a few 

 groups was there apparently any tendency toward a development of 

 bony excrescences from the squamous portion of the meatus — though 

 the incidence and proportions as given in the table for this item would 

 probably be augmented somewhat if an examination of the whole 

 squamous part were always possible ; and that the floor of the meatus 



