226 



THE HEAD AND NECK 



with the lateral ventricles through the inter-ventricular foramina 

 of Monro. The whole of this system is lined by ependyma, a 

 thin membrane covered by ciliated columnar epithelium. 

 The cerebro- spinal fluid fills the ventricular system, and normally 

 drains away through certain apertures in the walls of the 

 ventricles into the subarachnoid space. The largest of these 

 apertures (the foramen of Magendie) is placed in the lower 



Higher motor centres for lower limb 



Central sulcus 

 Cerebral aqueduct 



Higher 

 visual centres 



Sulcus cinguli 



| Corpus callosum 



Interventricular foramen 

 (of Monro) 



cut 



ophysis 



Cisterna interpeduncularis 

 Midbrain 

 s 



edian aperture of fourth ventricle 

 (foramen of Magendie) 

 Medulla oblongata 



x 'Cisterna cerebello-medullaris 

 ""-, Central canal of spinal medulla 



FIG. 69. Median Section through the Brain. The arachnoid 

 is shown in blue. 



Fourth ventricle 



part of the roof of the fourth ventricle. The cerebro-spinal 

 fluid passes through the arachnoid by a process of osmosis into 

 the sub-dural space, where it mixes with the sub-dural fluid 

 and ultimately becomes absorbed. It is derived from the 

 veins of the chorioid plexus, which invaginate the ependyma 

 and project into the cavities of the lateral and fourth 

 ventricles. 



Congenital Hydrocephalus is said to be due (i) to an in- 

 crease in the amount of cerebro-spinal fluid secreted or (2) to 

 a diminished rate of absorption. On the ground of the former 



