Chap. 27.] ke Pia Maief. 269 



the dura mater and the internal lamina of the pia ma- 

 ter, by means of blood-veflels, but in other parts it is 

 quite feparate from both. It is fpread uniformly over 

 the furface of the brain, inclofmg all the convolutions, 

 but not entering between any of them* 



On the contrary, the internal and mod confiderable 

 lamina of the pia mater is not only infinuated into the 

 numerous folds and circumvolutions of the brain, but 

 is continued into its cavities, performing the important 

 office of conveying the blood-veffels to that delicate or- 

 gan in fuch a minute ftate of divifion, that their pulfa- 

 tion cannot be prejudicial to its functions. 



The brain completely fills the cavity of the cranium, 

 and its form therefore correfponds with it \ it is con- 

 vex above, irregular below, and flat at the fides. Un- 

 der the general name of brain, or encephalon, are in- 

 cluded the cerebrum, which occupies the upper and 

 largeft portion of the cranium, and the cerebellum, 

 which is feated in its lower and pofterior part, under 

 the tranfverfe feptum. The cerebrum is divided longi- 

 tudinally at its upper part, by the falx, into its twohe- 

 mifpheres. The irregular furface of the cranium be- 

 low divides each hemifphere into three lobes. The 

 anterior lobe is lodged on the orbital procefTes of the 

 os frontis ; the middle lobe lies in the middle fofias of 

 - the bafis of the cranium ; the pofterior refts on the 

 tranfverfe feptum over the cerebellum. The cere- 

 bellum is itfelf divided into two hemifpheres by the 

 .Imall falx. 



The component matter of the brain is of two kinds,- 

 a greyifli matter, which is for the mod part placed 

 without, and is therefore called the cortical, and a white 

 matter called the medullary, which is generally fituated 

 within. The cortical part chiefly accompanies the 

 convolutions of the brain j the medullary is entire, and 



ieems 



