116 THE BRAIN. 



fibres. The two sets intersect each other, having spaces 

 termed ventricles, while the converging fibres constitute 

 the Commissures of the Brain. 



The Brain, (Fig. 16,) filling the cavity of the Cranium, 

 is, like all other portions of nervous tissue, composed of 

 white and gray matter, but differently arranged, the 

 white occupying the centre, while the gray covers the 

 surface. We however find both kinds, in variable quantity, 

 interspersed throughout the Brain. The Brain is divided 

 into Cerebrum and Cerebellum. The former is again di- 

 vided into hemispheres, and these subdivided into lobes. 

 The surface of the Cerebrum is thrown into convolutions, 

 which are regarded as the organs of intelligence. 



The relation which the Brain, Spinal Marrow, and their 

 nerves, sustain to each other is so intimate as to unite 

 them all in a circle of communication and action. The 

 Brain, forming the central organ of perception, receives 

 the impressions the Spinal Marrow and nerves of Sen- 

 sation convey these impressions, while the nerves of Mo- 

 tion carry out the mandates of the Brain to the different 

 muscles of the body thus forming a circle of conduc- 

 tion, perception, and action. 



This tissue has likewise the closest relation with all the 

 organs and functions of the body. 



The second great division of the nervous system is that 

 of organic Life. It belongs to the trunk, is connected with 

 the organs of nutrition, consists of a great number of 

 G-anglia, whence it is called the Granglionic system. These 

 Ganglia are found in the neck, chest and abdomen, and send 

 off an infinity of filaments, which^ running together and in- 

 terlacing, constitute the various plexuses, following and 

 intimately surrounding the arteries, in their route to the 

 several organs. This system is also styled the Sympathetic, 

 as it connects the different parts of the body together 

 Splanchnic, from its being so largely associated with the 

 various viscera and, more recently, Automatic, from being 

 regarded as self-moving and the original source of nervous 

 power to every other part. 



