Diseases of the nervous system / edited by Archibald Church.

Date:
1908
Catalogue details

Licence: In copyright

Credit: Diseases of the nervous system / edited by Archibald Church. Source: Wellcome Collection.

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    ary of which is formed by the corpora quadrigemina, the lateral limits by the structures beneath, the red nucleus, the lemniscus tracts, etc., while the cere- bral peduncles are found upon the floor. In the region of the metencephalon these canals dilate and form the fourth ventricle, the so-called rhomboid fossa, the roof of which is formed by a thin membrane, the tela chorioidea posterior, above which we find the layers of the cerebrum developed from the dorsal wall of the occipital vesicles; this structure with its arms which extend to the other parts of the brain forms the lateral boundary of the fourth ventricle, while the mass of the pons and the medulla oblongata spreads out caudally toward the base. In the medulla the fourth ventricle gradually narrows and becomes the central canal of the spinal cord, and in various ways, in adult man being partly obliterated, extends through the entire length of the cord, and terminates in the conus terminalis. After the development of the central nervous system of man in its exter- nal forms, in the adult human being the greatest interest centers in the forma- tion of the fossce and convolutions from the pallium. A few so-called “ transi- tory fossae99 develop from the second to the third month but subsequently dis- appear, after which, in the fifth month, the first permanent fossa, the Sylvian fossa, is formed by that portion of the pallium which communicates with the corpus striatum, the island of Reil, which is slower than the remaining parts of the pallium in growth. At first there is a flat depression which, by the rapid extension of the remaining pallium, constantly becomes deeper so that at about the middle of the fifth month the anterior and posterior por- tion of the fossa Sylvii is well developed while the rest of the brain is still Fig. 3.—Brain of a Human Fetus at the End of 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 fossae, which, however, are still primitive but permit the principal convolutions of the perfect brain to be distinctly recognized. Even to-day the importance of the formation of convolutions and fossae has not been positively determined. Although it is generally maintained that the formation of fossae in the cerebrum occurs only in the higher animals and in these constantly undergoes greater development, and that, as we have just seen, this cerebral furrowing in the embryo of man takes place compara-
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