CHAPTER XV. 

 THE BRAIN. 



THE muscles are the executive organs ; but the seat 

 of the will is the brain. 



If models of the brain can be obtained, they should 

 be carefully studied. If not, the accompanying figures 

 may be used in their stead. 



The Coverings of the Brain. There are two readily 

 distinguishable coats of the brain, the dura mater, a tough 

 membrane, adhering more or less closely to the inside 

 of the skull ; and the pia mater, next to the brain, a much 

 thinner membrane, traversed by blood tubes, and dipping 

 down into the grooves between the convolutions of the 

 cerebrum. 



The Parts of the Brain. The larger and upper part 

 of the brain is the cerebrum ; below and back of this is 

 the smaller cerebellum ; the part of the spinal cord within 

 the cranium is generally reckoned as part of the brain. 



The Cerebrum. The cerebrum consists of two lateral 

 hemispheres, separated by a deep median groove. The 

 surface of the cerebrum is in irregular ridges, the con- 

 volutions. The outside of the brain consists of gray 

 matter, whereas the outside of the spinal cord is white. 

 The inner part of the brain is white, and the two halves 

 are connected by a broad band of white matter, which 

 consists of many white fibers. 



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