Dr Stone oji the Frontal Sinus. 88 



hausted between the cranial tables ; which, after all, amounts to 

 no more than a bare acknowledgment that such cavities do ex- 

 ist. Soemmering, in speculating on their origin, hazards the 

 supposition, that bony substance, or diploe, is first deposited, 

 and then absorbed for the purpose of leaving these spaces ; an 

 explanation which appears somewhat clumsy, and which, at any 

 rate, he did not support by any corroborative testimony. Ac- 

 kermann has had recourse to a theory which appears to me still 

 more fanciful and untenable : he states, that air being drawn 

 up, in the act of inspiration, through the nasal passages, insinu- 

 ates itself between the tables of the frontal bone, and, by striking 

 against them, mechanically separates them from each other; 

 which hypothetical explanation is refuted at considerable length, 

 under the article Crane, in the Dictionnaire des Sciences Medi- 

 cales. It is remarkable that even Sabatier attaches some import- 

 ance to this vague surmise ; — but, without proceeding to adduce 

 other theories which have been proposed to explain their origin, 

 and which appear alike unsatisfactory, I may briefly premise, 

 that the one which has been recently propounded by the learned 

 and ingenious Dr Milligan, appears to me sufficiently satisfac- 

 tory ; yet, before explaining how his views are coincident with 

 my observations, I must state, which I shall do briefly, the ge- 

 neral results of my inquiries concerning the growth of the head 

 at different periods of life. 



It is evident that the most conclusive method of obtaining in- 

 formation on this subject, would be to measure the same head 

 at diff'erent successive ages ; but this, for obvious reasons, has 

 not been hitherto in my power. To supply this desideratum, 

 therefore, I ascertained the extent of the required dimensions of 

 the head in a great number of subjects of the same age, and then 

 found the average extent of each dimension at that period of life. 

 I then arranged in another class the heads of persons of the same, 

 but of a more advanced age; and, after obtaining the individual, 

 found the average dimensions of these ; then, by comparing 

 these averages together, deduced the general amount of these 

 dimensions at the ages chosen, and their average increment be- 

 tween the periods allotted to each class. It appears by this in- 

 vestigation, that, during the first four years of life, the head in- 

 creases equally in all its directions, i. e, in its longitudinal, trans- 



r2 



