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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXII. 



These figures show again, as did .similar data with the anterior fossas 

 (q. v.). that in the fetuses and 3^oung the proportion of cases where 

 either tlie right or the left cavity is longer is much smaller than in the 

 adults, and points to the fact that irregularities are to a large extent of 

 later development. In the anthropoid apes I find a higher differen- 

 tiation in the middle fossae than in the human young, similarl}' as with 

 the anterior cavities. 



The actual differences between the middle fossae ranged thus: 



Absolute differences in length of the middle fossse; right fossa the longer in cases: 



« 6.5 mm. 

 Absolute differences m length of the middle fossa: ; left fossa the longer in cases: 



The conditions disclosed by the above figures are such that almost 

 the exact words which were used in describing the differences in the 

 anterior fossae are applicable. In this case, as there, the range of dif- 

 ferences is somewhat greater with the right fossa; the inequalities 

 are smaller in the young; they show a range of fair extent in the 

 anthropoid apes, though the skulls are less than half the size of full- 

 grown human crania, and they are ver}^ small in the monkeys and 

 other mammals. 



The form of the skull maj^ have some slight connection in this case 

 with the differences in the length of the cavities. In three of the series 

 (white females, Indians, negroes) the right fossa is longer than the 

 left in a larger percentage of the dolichocephals than of the brach}^- 

 cephals (in dolichocephals in 50, 70, 47 per cent; in brachycephals, 

 rcspectivel}", in 33, 50, and 33 per cent of cases). Race may also be a 

 factor, for a larger proportion of cases with longer right middle fossa 

 is found among the Indians than in any of the other series. As to sex, 

 no influence on the difference between the lengths of the two middle 

 cavities is apparent. 



A comparison of the inequalities in length in the middle with those 

 of the anterior fossas reveals the fact that these disproportions can be 



