VASOMOTOR SUPPLY OF THE ORGANS. 



619 



especially the superior longitudinal sinus. Each body is a minute, 

 pear-shaped protrusion of the arachnoidal membrane into the inte- 

 rior of a sinus, as represented schematically in Fig. 260. Through 

 these bodies the cerebrospinal 

 liquid is brought into close 

 contact with the venous 

 blood, the two being sepa- 

 rated only by a thin layer 

 of dura and the very thin 

 arachnoid. The number of 

 the Pacchionian bodies is 

 hardly sufficient to lead us 

 to suppose that they have a 

 special physiological impor- 

 tance. The cerebrospinal liq- 

 uid found in the subarach- 

 noidal space and the ventri- 

 cles of the brain is a very 

 thin, watery liquid having a 

 specific gravity of only 1.007 

 to 1.008. It contains only 

 traces of pr^ceins and other 

 organic substances, which may vary under pathological condi- 

 tions. It is thinner and more watery than the h^mph, resembling 

 rather the aqueous humor of the eye. The amount of this fluid 



Fig. 259. — Diagram to show the location 

 of the cisternsB and canals of the subarach- 

 noidal space. — {Poirier and Charpy.) 



Fig. 260. — Schema to show the relations of the Pacchionian bodies to the sirmses; 

 d, d, Folds of the dura ms-ter, inclosing a sinus between them; v.b., the blood in the 

 sinus; a, the arachnoidal membrane; p, the pia mater; Pa., the Pacchionian body as 

 a projection of the arachnoid into the blood sinus. 



present normally is difficult to determine. Various figures have 

 been given, but it is usually stated to amount to 60 to 80 c.c. If 

 these figures are correct it evidently does not form a thick envelope 

 to the nervous system. Under abnormal conditions (hydroceph- 



