DESCRIPTION. 29 



supports the larger divisions of this soft and tender organism : and 

 between its layers it contains the great channels of venous blood 

 known as the sinuses of the brain. 



We see then that the consciousness is physically nourished from 

 without, as the brain is nourished by the blood of the pia mater; that 

 it is physically movable, or can assume varieties of shape and state, 

 as the floating brain can move its person upon its fluids, and speci- 

 fically upon the arachnoid bed : we also observe that the conscious- 

 ness, like the brain, is limited, the dura mater and the skull being 

 the emblems of that limitation. 



The brain is supplied with blood by the carotid and vertebral arte- 

 ries. The carotids are the first great vessels which issue from the 

 stem of the arterial tree, and they supply the cerebrum with the first 

 blood of the heart. The vertebrals are the first streams from the 

 subclavians, which supply the arms with blood. Thus the first blood 

 of the body and the limbs is alienated to the brain. Its veins, which 

 bring back towards the heart the blood that has passed through the 

 before-mentioned arteries to the pia mater and substance of the brain, 

 empty themselves into certain peculiar channels contained in the lay- 

 ers of the dura mater, and termed the sinuses of the brain ; which 

 sinuses communicate with each other at last, and pass out of the skull 

 by a bend or curve where the carotid enters; there constituting the 

 internal jugular vein, which carries the first considerable stream that 

 is returned to the heart. 



The cerebral globe is divided into two halves, and each of these 

 into lobes; the lobes again being subdivided into convolutions, which 

 have furrows between them that dip down into the brain, and are 

 covered by the pia mater. By means of these foldings, the surface 

 of the cerebrum is much increased, and space is economized ; this 

 folding of surfaces into solids being one of the principles of the body, 

 whereby distances are brought together, and association or organiza- 

 tion is promoted. In proportion to the number of these twists or 

 convolutions is the power of the brain. The mind's revolvings are 

 here represented in moving spirals, and the subtle insinuation of 

 thought, whose path lies through all things, issues with power from 

 the form of the cerebral screws. They print their shape and make 



