VASCULAR REGULATION IN THE BRAIN 



able minute branches. These capillaries after frequent communication with 

 one another enter the brain in a very uniform and equable distribution. 

 The arrangement of the veins within the cranium is also peculiar. The large 

 venous trunks or sinuses are formed so as to be scarcely capable of change 

 of size; and composed, as they are, of the tough tissue of the dura mater, 

 and in some instances bounded by the bony cranium, they are not com- 

 pressible by any force which the fulness of the arteries might exercise through 



FIG. 208. Showing the Origin and Course of the Vascular Nerves for the Head. (Modified 



from Moret.) 



the substance of the brain. Nor do they admit of distention when the flow 

 of venous blood from the brain is obstructed. 



The mechanical conditions in the brain and skull formerly appeared 

 enough to justify the opinion that the quantity of blood in the brain must 

 be at all times the same. But it was found that in animals bled to death 

 without any aperture being made in the cranium, the brain became pale and 

 anemic like other parts. And in death from strangling or drowning, there 

 was congestion of the cerebral vessels; while in death by prussic acid, the 

 quantity of blood in the cavity of the cranium was determined by the position 

 in which the animal was placed after death, the cerebral vessels being con- 

 gested when the animal was suspended with its head downward, and com- 



