Diseases of the Nervous System

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PRENATAL DISEASES AND DEVELOPMENTAL DEFECTS OF THE NERVOUS SYSTEM INTRODUCTION.—-We may divide the abnormalities of the nervous system which arise before birth into two chief groups. In one, some part of the nervous system is absent, or incompletely formed, and it is evident that we are not dealing with destruction as a result of injury or disease, but with a defect of development. In the second group, we find evidence that the nervous system has developed up to a certain point and that destruction of nervous tissue has then taken place. It is not always easy to separate these two groups, for injuries inflicted during the course of development may not only destroy the affected structure, but may inhibit the development of closely related structures. The defects of development, apparently, are much more common than the intrauterine diseases. The former group will be discussed first. We shall learn in the following pages that there is a great variety of defects of the nervous system, a