Dr Stone on the Frontal Simis. S?7 



ly, to be the average depth of the frontal sinuses. Such, then, 

 is the connection which evidently exists between the general 

 growth of the head and the formation of these sinuses. 



The average extent of these sinuses next claims consideration, 

 on which subject anatomists have not recorded hitherto any de- 

 finite observations. Albinus describes them as " cavemas mag- 

 nas amplissimas prope nasum ;'*'' and extending upwards and la- 

 terally over the orbits, as far as the middle of the superciliary 

 ridge. Ruysch states that they are often very large, and cites 

 the case of a puella gigantea, in whom they extended above the 

 coronal suture, and some way between the tables of the parietal 

 bones. Winslow, Lieutaud, and Palfin, state they vary much in 

 different individuals ; but it does not appear that they paid any 

 attention to their average extent. Dr Monro (the present Pro- 

 fessor) gives, in his Elements of Anatomy, some measurements 

 of the frontal sinuses ; but the sinuses to which he refers, are 

 stated to have been unusually large, consequently they do not 

 represent the universality of Nature. I have measured these si- 

 nuses in upwards of a hundred crania, and consider that the fol- 

 lowing may be regarded as their average extent. 1st, Their 

 extent in height is 1 inch ^'^^ths; — 2d, their extent in breadth 

 is 2 inches ^*oths, this is, for each sinus; — and their extent in 

 depth /^ths of an inch. 



Such was their average size in the crania examined by me ; 

 but, of course, in some individual cases they may be much smal- 

 ler, or much larger. I shall conclude this memoir by stating 

 the peculiarities by which these frontal sinuses are characterised, 



1. The frontal sinuses originate under each os unguis, and thence extend, 



in the manner described by Albinus, laterally and vertically, over the 

 orbits. Their origin at this point is evidently owing to the extension 

 of the mucous membrane lining the nasal cavities, which creeps from 

 under this bone, to extend between the cranial tables. 



It is remarkable that Gagliardi has not only erroneously described, 

 but has given a plate to his work, in which these sinuses are repre- 

 sented in an erroneous position *. 



2. The sinus is most commonly divided by a septum, which generally runs 



down the mesial line ; but often inclines much to the right, or much 

 to the left side. In illustration of this, I may refer to the Anatomical 

 Museum of the University (Dr Monro's), wherein will be found five 

 skulls sawn open, to show these sinuses, rather large. In No. 104, 



• Gagliardi Anatom. Ossium, 1723. 



