Identifier: textbookofphysio1916howe (find matches)
Title: A text-book of physiology : for medical students and physicians
Year: 1916 (1910s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Medicine
Publisher: Philadelphia and London : W. B. Saunders Company
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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y, the granular layer (3 in Fig. 81), the supra-granular layer (2), comprising the pyramidal cells external to the * Cajal, Les nouvelles idees sur la structure du systeme nerveux, etc.,Paris 1894. t For a summary of these views consult Bolton, Brain, 1910 and 1912,or Further Advances in Physiology, Hill, London and New York, 1909;Van Valkenburg, Folia neurbbiologica, 1910, 4, 335. GENERAL PHYSIOLOGY OF THE CEREBRUM. 187 granular layer, and the infragranular layer (4 and 5), comprisingthe pyramidal and fusiform cells internal to the granular layer.Comparison of the cerebral cortex in the brains of the differentvertebrates indicates that the supragranular cells have appearedrelatively late in the phylogeny of the vertebrates, and havereached their greatest development in the human brain. Thesuggestion occurs, therefore, that these cells have a different func-tional significance from those in the infragranular layer. It hasbeen supposed that the supragranular cells mediate the so-called
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Fig. 84.—A-D, Showing the phylogenetic development of mature nerve cells in aseries of vertebrates: a-e, the ontogenetic development of growing cells in a typical mam-mal (in both cases only pyramidal cells from the cerebrum are shown); A, frog; B, lizard;C, rat; D, man; a, neuroblast without dendrites; b, commencing dendrites; c, dendritesfurther developed; d, first appearance of collateral branches; e, further development ofcollaterals and dendrites.—(From Ramon y Cajal.) higher psychical processes, which characterize man and the relatedmammalia as compared with the lower vertebrates. The infra-granular cells, on the other hand, constitute a primitive layer whichhas obvious connections, through projection fibers, with the under-lying parts of the brain and of the body at large. These cellsform, therefore, a mechanism through which the brain is connecteddirectly with the rest of the body, and through which the older 188 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. instinctive reactions

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