NO. 1521. MEASUREMENTS OF CRANIAL FOSS.E—HRDLICKA. 191 



only in a limited number of cases compensatory in nature; in a large 

 percentage of the crania there is no trace of a correlation. The fol- 

 lowing conditions exist in this regard among the human adults: 



Per cent 

 of eases. 



Anterior fossae of equal length, middle fossae of equal length 4. 3 



Anterior fosste of equal length, right middle fossa longer than left 10. 9 



Anterior fossse of equal length, right middle fossa shorter tlian left 5. 4 



Eight anterior fossa longer than left — 



middle foss;e equal 20. 7 



right middle fossa longer than left 29. 3 



right middle fossa shorter than left 13. 



Right anterior fossa shorter than left — 



middle fossae equal 4. 3 



right middle fossa longer than left 8. 7 



right middle fossa shorter than left 3. 3 



The only two series of cases where a compensation between the 

 length of the anterior and middle fossa of the same side may exisit 

 (that is, "the right anterior fossa longer than the left — the right middle 

 fossa shorter than the left," and the opposite) embrace only 13 and 

 8.7, in total 21. T per cent, or about one-tifth of all the skulls exam- 

 ined. On the other hand, a greater length of both the anterior and 

 middle fossa on the same side was present in 29.3 per cent (right side) 

 and 3.3 per cent (left side), in all 32.6 per cent, or almost one-third, of 

 the crania. These facts show that the dimensions of one pair of the 

 fossse in question are to a large extent independent of those of the 

 other pair, which make it plain that they are not due to conditions 

 inherent in the bones themselves, but to those pertaining to the brain. 



The relations which the mean length of the two middle fossae bear 

 to the size of the skull are indicated in the figures below. As with the 

 anterior cavities, the size of the skull was judged from the mean of its 

 greatest length and breadth; the fossae were contrasted with the great- 

 est external as well as the mean ventral length. The specimens 

 selected for this comparison were the same as with the frontal fossaj 

 on a similar occasion. 



Average relations of the mean length of the two middle foss:v to the greatest dorsal and mean 

 ventral length of the skull {each of these dia)neters being each taken as 100), in the largest 

 and smallest skidls of the series. 



