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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXII. 



all probability compensatory relation with the latter. The following 

 conditions existed in this regard among the human adults. 



Per cent 

 of cases. 



Anterior (a)+mi(ldle {m) fossa? of equal length, postero-superior (ps) fossae of 



equal length 



a-\-m of equal length, right ps longer than left 1.1 



a-\-m of equal length, right ps shorter than left 7.6 



Right a + »i longer than left, ps equal 2.2 



Right a-\- m longer than left, right ps longer than left 12. 



Right a-\-m longer than left, rightps shorter than left 56. 5 



Right a-\-m shorter than left, ps equal 4. .3 



Right a + m short ^r than left, right ps longer than left 6. 5 



Right a + ™ shorter than left, right ps shorter than left 9. 8 



In 63 (56 + 6.5) per cent of the cases the length of the postero- 

 superior fossa stood in an apparently compensatory relation to the joint 

 length of the two other cavities of the same side. A certain propor- 

 tion of this number of cases, very probably the majority, represents 

 a true compensation, the rest being due to conditions inherent in the 

 posterior fossie themselves or, more properh', in peculiarities of those 

 portions of the cerebrum which fill them. In 2 1.8 (right 12, left 9. 8) 

 per cent of the skulls the postero-superior fossa on one side was 

 longer, notwithstanding the fact that the sum of the length of the mid- 

 dle and anterior cavities on the same side was also longer than that on 

 the opposite side. In several of these cases all the three cavities on 

 the same side were individually longer than those on the other side of 

 the same skull. In no case among the 92 adult human crania were all 

 the three fosste of one side exactly equal to those opposite. The ten- 

 dency to a greater length of the left postero-superior fossa is very 

 pronounced. It accompanies, in the skull, and is the main manifesta- 

 tion of, the prevalent greater length of the left cerebral hemisphere. 



The relations born ])y the mean length of the postero-superior fossae 

 to the size of the skull, the latter judged as before, from the mean of 

 its greatest length and breadth, are indicated ])eneath, the specimens 

 represented being the same as with the frontal and middle foss;e on 

 the occasion of similar comparison. 



Average relation of the mean length of the two postero-superior fossse to the greatest dorsal and 

 mean ventral length of the skull ( each of these diameters being taken as 100) in the largest 

 and smallest skulls of the series. 



