562 



CEREBRO-SPINAL MEMBRANES. 



that in the floor of the fourth ventricle, contain caudate cells, many of them of the 

 largest size, with long appendages, and deeply coloured with pigment. (Hannover, 

 Rech. Microscop. sur le Systeme Nerveux. Copenhagen, 1844). 



The pineal body, like the pituitary body, has already been sufficiently described. 

 The deep connection of some of the cranial nerves with the basal parts of the cere- 

 brum, as well as that of others with the remaining portions of the encephalon, will 

 be referred to in the description of these nerves. 



THE MEMBRANES OF THE BRAIN AND SPINAL CORD. 



The cerebro-spinal axis is protected by three membranes, named also 

 meninges. They are : 1. Au external fibrous membrane, named the dura 

 mater, which closely lines the interior of the skull, and forms a loose sheath 

 in the spinal canal ; 2. An internal areolo-vascular tunic, the pia mater, 

 which accurately covers the brain and spinal cord ; and 3. An intermediate 

 serous sac, the arachnoid membrane, wLich, by its parietal and visceral 

 layers, covers the internal surface of the dura mater on the one hand, and 

 is reflected over the pia mater on the other. 



THE DURA MATER. 



The dura mater, a very strong dense inelastic fibrous tunic of considerable 

 thickness, is closely lined on its inner surface by the outer poition of the 



Fig. 384. 



Fig. 384. THE CRANIUM OPENED TO snow THE FALX OP THE CEREBRUM, AND TENTORIUM 

 OF THE CEREBELLUM. 4 



a, right side of the falx cerebri ; a', its anterior narrow part attached to the crista 

 galli ; 6, tentorium cerebelli of the right side, united to the base of the falx cerebri 

 from 2 to 3, in the Hue of the straight sinus, and attached to the superior border 

 of the petrous bone between 3 and 3' ; b', aperture between the right and left divisions 

 of the tentorium for the isthmus cerebri ; 1, 1, the superior longitudinal sinus; 2, 2, the 

 inferior ; 3, 3, the lateral sinus; 3, 3', the superior petrosal sinus j 3', is close to the 

 anterior clinoid process. 



