. Human physiology : designed for colleges and the higher classes in schools, and for general reading. which lies outsideof this next to the bony covering is called the dura mater, orhard mother. The names are entirely inappropriate, for thelatter serves as a protection to the brain, and the former a vehicle or medium for the entrance of the bloodvessels into the brain. There is another membrane lyingbetween these which is called the arachnoid membrane, be- 13 146 HUMAN PHYSIOLOGY. Gray and white substance. Proportions and arrangement. cause in its tenuity and delicacy it resembles t
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. which lies outsideof this next to the bony covering is called the dura mater, orhard mother. The names are entirely inappropriate, for thelatter serves as a protection to the brain, and the former a vehicle or medium for the entrance of the bloodvessels into the brain. There is another membrane lyingbetween these which is called the arachnoid membrane, be- 13 146 HUMAN PHYSIOLOGY. Gray and white substance. Proportions and arrangement. cause in its tenuity and delicacy it resembles the spidersweb. It is one of the serous membranes, and it serves a& aprotecting envelope to the brain, and at the same time by itsserum, keeps this organ bedewed with moisture over its wholesurface. 231. The substance of which the brain is composed is verysoft, something like blanc-mange. It is the softest organ inthe body. It is not uniform throughout in color. All aroundthe white inner part of the brain there is a thick layer of graysubstance. In Fig. 74 you have a horizontal section of SECTION OF THE BRAIN. brain, showing the proportions and arrangement of the grayand the white substances. As the gray substance dips down,as you see in the figure, into all the furrows, its extent isgreater than you would suppose at the first view. In themiddle is represented the broad connection which existsbetween the two hemispheres of the brain. You observe in THE NERVOUS SYSTEM. 147 The grny substance made of cells, the white of tubes. Fig. 73, and Fig. 74, that there is no apparent arrangement ofthe external parts of the brain, which would give countenanceto the idea of the phrenologist, in relation to a division intoparticular organs. The convolutions, so far from presentingany well defined arrangement, are exceedingly irregular. 232. The gray substance, which is sometimes called thecortical (bark-like) substance, because it surrounds the whitecentral part of the brain, is made up,
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