326 PHYSIOLOGY AND HEALTH. 



somewhat pulpy; it is of very delicate texture, and can be 

 easily separated by the fingers. The outer portion is of a gray 

 color, and is called the cortical part. The inner portion is of a 

 white color, and called the medullary part. 



It is supposed, by some v that these two parts of the brain 

 have different offices ; that one is the organ of the mental 

 operations and the affections ; that, through it, the mind acts 

 and the feelings operate, while the other is supposed to be 

 the organ of sensibility, and, upon that, impressions from the 

 sensory nerves are recejved, and in it sensations are created 

 and perception takes place, and that it holds the commu- 

 nication with all the rest of the body. But how far this sup- 

 position is true is not shown, nor is it necessary for us to know. 



748. The brain is covered and held together by three mem- 

 branes. The inner and the middle of these membranes are 

 very delicate, and give the brain a sofUcushion to lie between 

 it and its bony enclosure. The outer membrane is thick and 

 very strong, and would hold the brain in its position and 

 retain its shape even when removed from the skull. These 

 membranes surround, the brain on , all its sides, above and 

 below. The inner and soft menabranes dip. into the brain 

 between the convolutions or little lobes, and separate them 

 superficially. 



The brain is divided into two parts, called the right and 

 left lobes, (Fig. LXII. a, b,) which are exactly alike on the 

 two sides. These are separated by a partition wall ? or a wing 

 (Fig. LXII. c, c) of the same membranes that cover the organ. 

 This partition runs, from the -front to the back of the skull, 

 and almost to the bottom of the brain. It supports the two 

 lobes in their position, and prevents-them from pressing upon 

 each other when we lie down. 



749. The brain is also divided into two other parts the 

 greater or cerebrum, and the lesser or cerebellum. The greater 

 occupies almost the whole of the cavity of the head above 

 and in front. The lesser is behind arid4jelow, just above the 

 neck. A wing of the membran^g extends across the skull 

 from side to side behind, and separates these two. parts of the 



