I 12 



THE NERVOUS SYSTEM 



The additional support which they gain in this way is 

 required, for their walls are extremely thin and consist of 

 little more than a lining of endothelium. On this account 

 severe haemorrhage occurs when a sinus is wounded, as its 

 walls do not collapse like those of other veins. The cranial 



Corpus callosu 



Septum pellucidum 



Interventricular foramei 



Lamina terminalis 



Ooulo-motor nerve 

 Pon 



__ Middle'commissure 



' _ Pineal body 



"" _ _ -Corpora quadrigemina 



^, Cerebral aqueduct 



(of Sylvius). 



^ Fourth 

 ventricle 



_ _ Central canal of 

 ~" spinal medulla 



FIG. 54. Median Sagittal Section through the Brain-Stem, showing the 

 third and fourth ventricles and their connexions. 



sinuses establish numerous connexions with the veins outside 

 the skull, and these communications are of great practical 

 importance, because, as they possess no valves, they afford 

 channels for the spread of septic thrombi. 



The Superior Sagittal (Longitudinal) Sinus lies in the 

 upper border of the falx cerebri. It begins anteriorly at the 



