202 HEAD AND NECK 



are from without inwards (i) the dura mater; (2) the 

 arachnoid ; and (3) the pia mater. 



When the skull-cap is detached, the outer surface of the 

 dura mater, as it covers the upper surface of the cerebral 

 hemispheres, is exposed. It is rough, and dotted over with 

 bleeding points. If a portion is placed in water, its roughness 

 becomes still more manifest, and is seen to be due to a multi- 

 tude of fine fibrous and vascular processes by which it is 

 connected with the deep surface of the bones. These have 

 necessarily been torn asunder in the removal of the skull- 

 cap. The bleeding points are most numerous along the 

 median line, or, in other words, along the line of the superior 

 sagittal sinus (O.T. longitudinal) ; and if the handle of the 

 knife is run from before backwards, so as to make pressure 

 along this line, a considerable quantity of blood will ooze out. 

 This shows that a number of small veins from the cranial 

 bones have been ruptured. The degree of adhesion between 

 the dura mater and the inner surface of the cranial bones 

 varies in different subjects and in different localities. In all 

 cases it is strongly adherent along the lines of the sutures, like 

 the pericranium externally; and, further, it is much more firmly 

 attached to the base than to the vault of the cranium. In the 

 child indeed, as long as the bones of the cranium are grow- 

 ing it is more adherent than in the adult ; and it is more 

 firmly bound to the bone again in old age. 



The dissectors should now clean the outer surface of the 

 dura mater with a sponge. They will then recognise the middle 

 meningeal artery upon each side, ascending in the substance 

 of the membrane, and sending off its branches in a widely 

 arborescent manner. It stands out in bold relief from the 

 membrane. If the skull-cap is examined, its inner surface 

 will be observed to be deeply grooved by the branches 

 of the artery and the veins which accompany and lie external 

 to them (Wood Jones). The meningeal arteries are not 

 intended for the supply of the membrane alone, as the name 

 might lead one to imagine. They are also the nutrient 

 vessels of the inner table and diploe of the cranial bones. 



Granulationes Arachnoideales (O.T. Pacchionian Bodies). 

 These granulations are almost invariably present, and, as a 

 rule, are best marked in old subjects. They are small granular 

 bodies, ranged in clusters on either side of the superior 

 sagittal (O.T. longitudinal) sinus, into which many of them 



