142 



BIOLOGICAL PHYSICS 



outflow, and one or all of which are simultaneously, or con- 

 secutively, available during the continuance, or existence, 

 of the normal physiological conditions, for the maintenance, 

 or preservation, of the normal intra-cranial pressure, and 

 the obviation of its undue increase, or diminution. 

 Supplementary to these we may include, or claim, the 

 Pacchionian bodies, or extensions of the arachnoid, which 

 traverse, or run through, the inner table of the calvarium, 

 more especially in certain regions of its upper aspect, as 

 completing the tutelary provisions of the great brain 

 drainage structures and mechanisms. 



ell 



*'** 



'cat 



FIG. 58. OUTLINE OF A LONGITUDINAL SECTION THROUGH THE BRAIN 

 OF A CHICK OF TEN DAYS. (After Mihalkovics.) 



h, cerebral hemisphere ; olf, olfactory lobe and nerve ; st, corpus striatum ; Iv, lateral 



bigemina ; amv, anterior medullary velum ; below which two last references are 

 the aqueduct of Sylvius and crura cerebri ; cbl, cerebellum ; z; 4 , fourth ventricle ; 

 bo.) basilar artery , ps, pons Varolii ; c// 4 , choroid plexus of the fourth ventricle ; 

 obi, medulla oblongata ; r, roof of fourth ventricle. 



The central cavities or ventricles of the brain drain into 

 and through the olfactory tracts, (Figs. 50, 51), bulbs, and 

 nerve extensions, anteriorly, into and through the in- 

 fundibulum, with its attached pituitary gland, and the 

 pineal gland centrally, and into and through the foramen 

 magnum posteriorly ; while the inter-meningeal or peri- 

 pheral brain spaces empty themselves through the con- 

 tinuous inter-meningeal spaces, which pass out through 

 the various openings in the skull wall along with 

 extensions of the meninges. 



In studying this system of drainage of the skull and 

 brain we have been much struck with what seems also to 

 have impressed other observers, without, however, their 

 apparently guessing the developmental necessities under- 



