72 BIOLOGICAL PHYSICS 



functional role assigned to it. These views we now more 

 and more consider altogether inadequate for the following 

 amongst other reasons, viz. because the quantity of the 

 fluid formed is much larger than is usually supposed, 

 being constantly produced by the entire secreting surfaces 

 and vasculature of the pia mater covering the brain and 



FIG. 6. SECTION OF THE POSTERIOR AND LOWER PARTS OF THE BRAIN 



WITHIN THE SKULL, TO EXHIBIT THE SUBARACHNOID SPACK AND 



ITS RELATION TO THE VENTRICLES. (After Key and Retzius.) 



The section was made in the frozen state, the cavities having been previously filled 

 with injection. 



i, i', atlas vertebra ; 2, odontoid process of the axis, 2' ; 3, third ventricle ; 4, fourth 

 ventricle; C, C, corpus callosum? C, gyrus fornicatus ; C, cerebellum; t, ten- 

 torium ; /, pituitary body; c, c, central canal of the cord ',fM, in the cerebello- 

 medullary part of the subarachnoid space, is close to the foramen of Majendie 

 by which that space communicates with the fourth ventricle. 



cord, besides the appendages known as the choroid 

 plexuses (of the two lateral, the third, and the fourth 

 ventricles), and because it fills the entire series of extra- 

 and intra-spaces of the various structural divisions of the 

 central (Figs. 6 and 7) and peripheral nervous system, the 

 which, therefore, necessitate the formation and continual 

 presence within the body of a very great quantity of 

 cerebro-spinal fluid, and the provision of a series of safety 



