EXTRACT XL 



ON THE DRAINAGE AREAS OF THE SKULL 

 AND BRAIN. 



THE drainage areas of the skull (Figs. 56, 57) may be 

 divided into three, in accordance with the fossal divisions 

 of its base, thus : the first, or anterior, draining the area 

 extending from the internal surface of the frontal bone to 

 the smaller wings of the sphenoid, and containing the 

 frontal lobes ot the brain with their contained lateral 

 ventricles ; the second, or middle, extending from the 

 smaller wings of the sphenoid bone to the insertion, or 

 attachment, of the tentorium cerebelli to the petrous 

 processes of the temporal bones and the internal trans- 

 verse ridges of the occipital bone, and draining the middle 

 and occipital lobes of the brain, with the contained third 

 ventricle, its appended hypophysis, and its superimposed 

 epiphysis, and the third, or posterior, extending from the 

 line of attachment of the tentorium cerebelli into the 

 petrous processes of the temporal bones in front to the 

 torcular Herophili behind, and draining the cerebellum, or 

 small brain, with the pons Varolii, medulla oblongata, and 

 fourth ventricle. Each of these areas possesses in its floor 

 drainage facilities for the discharge of surplus cerebro- 

 spinal fluid in the shape of openings, or foramina, which, 

 along the outgoing and incoming nerve and blood-vessel 

 structures, allow its free, but guarded, circulation, or 

 outflow. 



These areas represent three well-defined basal skull 

 terraces, (Fig. 56) or fossal plateaus, so to speak, on which, 

 as a foundation, the great cerebral textural divisions rest, 



