File:A text-book of physiology for medical students and physicians (1911) (14592099789).jpg

Identifier: textbookofphysio1911howe (find matches)
Title: A text-book of physiology for medical students and physicians
Year: 1911 (1910s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology
Publisher: Philadelphia, London, W.B. Saunders company
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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that the cells in this layer are especially con-cerned in the mediation of the higher psychical processes, while theinfragranular layer constitutes the mechanism for the more * Cajal, Les nouvelles idees sur la structure du systeme nerveux, etc.,Paris, 1894. t For a summary of these views consult Bolton, Brain, 1910, or Fur-ther Advances in Physiology, Hill, London and New York, 1909. 188 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. deeply impressed and primitive instinctive reactions. In thematter of lamination and distinct variations in size and appearanceof the strata of cells and fibers the human cortex shows a greaterdifferentiation than in the lower animals, and it is especiallycharacterized by a large development of what are known as asso-ciational areas (p. 221), particularly in the frontal lobe. Inthe third place, the central nervous system throughout the verte-brates is constructed upon the same lines, a mechanism of in-terconnecting neurons. There is a vast difference in the men-
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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 Ramdn y Cajal.) tal activity of a frog and a man, but the cortex of the cerebrum-shows a fundamental similarity in structure in the two cases.In addition to the variations in stratification or lamination referredto above one general distinction that comparative anatomy is ableto make is that in the higher animals the greater mental develop-ment is associated with a greater complexity and richness in the con-nections of the neurons. As shown in Figs. 84 and 85, the number ofprocesses, particularly the dendritic processes, is mu

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