Dr Stone on the Frontal Simis. 85 



seven years of age, the cranial tables are closely approximated, 

 but about that age {i. e, seven), the brain having attained its 

 full complement in size, the internal table is fixed in its position. 

 It is now the true osseous case of the full sized brain, and every 

 farther bony deposition takes place interstitially, which accounts 

 for thie superior hardness of this, which has been, consequently, 

 called the " vitreous " table of the skull. That the brain does 

 attain its full size at this early period of life, as was suspected 

 by the Wenzels, whose induction resting only on two cases, 

 proved nothing, was shewn by Sir William Hamilton, who not 

 only confirmed their opinion, by weighing the encephalon at 

 every age, but also shewed that the skull of a child does not 

 contain more sand than that of an adult, although the dimen- 

 sions viewed externally differed extremely. Now, at this period, 

 the brain requiring no further deposition of cerebral substance, 

 the branches of the external carotid arteries will assume a greater 

 activity of function *, and deposit that osseous matter which vi- 

 sibly increases the size of the facial and frontal bones. <L'on- 

 nected as the external table of the frontal bone is to the facial 

 bones, it is evident that when these facial bones start forward, the 

 frontal bone must accompany their development, which it does 

 without sympathizing with, or carrying along with it, the inter- 

 nal cranial table. What then happens ? It is clear that, when 

 the external table is gradually, in its advancement forwards, 

 separating from the internal table, an opening must be thereby 

 made, which would be filled with diploe; but that the vessels of 

 the Schneiderian membrane in contact at this point, irritated by 

 the change of position, and forming the membrane with much 

 greater vigour and rapidity than the bony diploe, extend into 

 this nasal cavity. Hence, as stated by Dr Milligan, a membrane 

 is speedily shot into the nascent hollow or sinus, which attach- 

 ing itself to the outer aspect of the vitreous table and the inner 

 aspect of the osseous table, forms an insurmountable obstacle to 

 the rudest diploe that might join these two layers, for it is a 

 mucous membrane, a class of tissues which scarcely ever forms 

 adhesions, and is here almost a shut sac, whose sides are every 

 day brought farther and farther asunder f."" 



• This law of " re-stagnation" is explained at length, and applied to other 

 phenomena of evolution, by Dr Milligan, in his valuable Appendix to his 

 Translation of Majendie. 



t Ibid. p. 604. 



