THE PIA MATER OF THE BRAIN. 13 



terior inferior cerebellar and the superior cerebellar with many 

 branches. 



The veins are more numerous than the arteries in the pia: 

 the internal and great cerebral veins, the veins of the chorioid 

 plexuses of the lateral, third and fourth ventricles and the basilar 

 vein; the cerebral veins, superior, medial and inferior; and the 

 superior and inferior cerebellar veins. All of them empty into 

 the sinuses (see page 2). 



Inferior quadrigeminal 



colliculus 



Fourth nerve 



Superior medullary 

 velum 



Restiform body 



Taenia 



Epithelial roof of 

 fourth ventricle 



Cuneate tubercle 



Clava 



Tuberculum cinereurr* 



Frenulum veli 

 Lateral fillet 



Fourth 

 ventricle 



Inferior medullary 

 velum 

 Chorioid plexus 



Median aperture 

 (Magendi) 



Obex 



Fig. 8. Roof and lateral walls of fourth ventricle, and its chorioid plexuses. 

 (After Morris's Anatomy,) 



Seven cerebral nerves 3d, 5th, 6th, yth, Qth, icth and nth 

 and the sympathetic supply the pia mater and its blood-vessels. 



The pia mater of the spinal cord has two layers, the outer of 

 which is the more vascular and contains the spinal arteries and 

 the tributaries of the external spinal veins. It forms three proc- 

 esses, namely, the anterior septum, which occupies the anterior 

 median fissure, and the ligamentum denticulatum of each side. 



