PROTECTIVE MECHANISMS OF THE NERVOUS SYSTEM 719 



before that this subarachnoidal space does not possess the same height 

 throughout the encephalon, but shows cistern-Hke enlargements at 

 different points, and especially over the corpus callosum and the optic 

 lobes. Over the upper and lateral aspects of the brain- it is very nar- 

 row. It has also been mentioned that it is traversed by numerous 

 fibers and bands, so that it really becomes subdivided into a multitude 

 of intercommunicating cells which in turn connect with the lateral 

 ventricles, the central canal and subarachnoidal space of the spinal 

 cord, the lymphatic channels of the cranial and spinal nerves, and the 



Fig. 360. — Right Lateral. Aspect of the Skull and Cerebral Hemisphere Out- 

 lined IN Black, with Orthogonal Projection of the Structures in the Median Plane 

 AND OF the Right Lateral, the Third and the Fourth Ventricles in Red. (Quain.) 



Man aged fifty-six years, o, nasion; b, bregma; c, lambda; d, union; t.r., temporal 

 ridge; s.c, sulcus centralis; s.p., Sylvian point. 



lymphatics of the nasal cavity and neck.^ It seems, however, that 

 the subdural and subarachnoidal spaces are not directly connected 

 with one another, although colored fluid injected into either cavity, 

 eventually reaches the lymphatics of the nasal cavity as well as those 

 of cranial nerves. 



Cerebrospinal fluid may be obtained from animals by introducing 

 a cannula through a slit in the sheath, of a nerve root into the subarach- 

 noid space of the spinal canal or by inserting it through the atlanto- 

 occipital membrane into the cistern-like enlargement of the subarach- 

 noid over the fourth ventricle. In man, it is now a rather common 

 procedure to introduce a hollow needle directly into the spinal, canal 

 1 Walter, Monatschrift fiir Psych, und Neurol., 1910, 28. 



