. Diseases of the nervous system . Island \ yJT , -| Occipital lobes Sylvian fossa Temporal lobes Fig. 3.—Brain of a Human Fetus at the End op the Fifth Month. quite smooth. At the end of the fifth month the central fossa is formed,and in the sixth and seventh months the remaining fossge, which, however, arestill primitive but permit the principal convolutions of the perfect brain tobe distinctly recognized. Even to-day the importance of the formation of convolutions and fossaehas not been positively determined. Although it is generally maintainedthat the formation of fossae in the cerebrum oc
. Diseases of the nervous system . Island \ yJT , -| Occipital lobes Sylvian fossa Temporal lobes Fig. 3.—Brain of a Human Fetus at the End op the Fifth Month. quite smooth. At the end of the fifth month the central fossa is formed,and in the sixth and seventh months the remaining fossge, which, however, arestill primitive but permit the principal convolutions of the perfect brain tobe distinctly recognized. Even to-day the importance of the formation of convolutions and fossaehas not been positively determined. Although it is generally maintainedthat the formation of fossae in the cerebrum occurs only in the higher animalsand in these constantly undergoes greater development, and that, as we havejust seen, this cerebral furrowing in the embryo of man takes place compara- MACROSCOPIC ANATOMY OF THE CENTRAL NERVOUS SYSTEM. Fig. Brain of a Human Fetus at SevenMonths. lively late, there is no absolute parallel between the mental development ofthe animal and the formation of fossae in the cerebrum. AYe know that someanimals have perfectly flat brains and that in others the brain is markedlyconvoluted, yet we are unable to determine a preponderance of cerebral activ-ity in the latter. Of course, inthe highest group of mammals,monkeys, from the lowest formsup to the anthropomorphic apes,there is an increasingly rich for-mation of fossae and convolutionswhich finally reaches its acme Lathe human brain. The importance of the fossaeunquestionably depends upon thegreatest possible surface distribu-tion of the cortex of the cerebrumwithin the limited space of thecavity of the skull. Althoughthe ganglion cells of the cortexconstantly increase in numbers bythe development of the brain, andspace is formed by their over-lapping each oilier in layers, thethickness of the cortex thus beingpermanently increased, a j
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectnervoussystem, bookye
