An elementary physiology and hygiene for use in upper grammar grades . how wonderfully themuscles are adjusted so as to act together, as, forinstance, when a boy throws a stone. This is sup-posed to be accomplished in part through the actionof the cerebellum. The Cerebrum. — The cerebrum is the largest part ofthe brain. Figure 65 shows that it is covered withdeep furrows which divide it into folds called convo-lutions. These folds are not exactly alike in all brains, 192 PHYSIOLOGY AND HYGIENE though the larger ones are almost always present. Thecerebrum is divided by a very deep furrow into t
An elementary physiology and hygiene for use in upper grammar grades . how wonderfully themuscles are adjusted so as to act together, as, forinstance, when a boy throws a stone. This is sup-posed to be accomplished in part through the actionof the cerebellum. The Cerebrum. — The cerebrum is the largest part ofthe brain. Figure 65 shows that it is covered withdeep furrows which divide it into folds called convo-lutions. These folds are not exactly alike in all brains, 192 PHYSIOLOGY AND HYGIENE though the larger ones are almost always present. Thecerebrum is divided by a very deep furrow into two parts, called the right and theleft hemispheres. The divisionis indicated in Figure 66. Thetwo parts are connected withthe body in such a way that theright hemisphere controls theleft side of the body, and theleft hemisphere the right sideof the body. The cerebrumis the part of the brain thatis active in thought and in theexercise of will power. Whatwe call the mind is centeredin the cerebrum. It is thecenter which starts and con-trols the activity of the Fig. 66. — The Nervous System. Showing the brain and the spinal cord with its nerves. THE SPINAL CORD A long, soft, white cord, called the spinal cord, startsfrom the lower end of the medulla (shown in Fig. 66},and passes down through the backbone or spine. Thevertebrae of the backbone protect the cord on all other words, the spinal cord runs inside the back-bone (see Fig. 43, p. 126). As may be seen from Fig-ure 66, the cord is not of the same thickness throughoutits length, but it becomes gradually smaller as it passesdown the back. At the lower end it divides into fine THE NERVOUS SYSTEM 193
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