File:A text-book of physiology, for medical students and physicians (1907) (14774848151).jpg

Identifier: textbookofphysio1907howe (find matches)
Title: A text-book of physiology, for medical students and physicians
Year: 1907 (1900s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Physiology
Publisher: Philadelphia, London, W.B. Saunders Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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s system throughout \\)v verte-brates i constructed upon the same lines, a mechanism of intercon-necting neurons. There is a vast difference in the mental activityof a frog and a man, but the cortex of the cerebrum shows a funda-mental •iiiiil.-irii ■ in :-i met ure in the two cases. The chief differencethai comparative anatomy is able to show is that iu the higher I (,i i .,u .iii mI.y bui la structure du systeme nerveux, etc.,Paris, is!)t. GENERAL PHYSIOLOGY OF THE CEREBRUM. 187 animals the greater mental development is associated with a greatercomplexity and richness in the connections of the neurons. Asshown in Figs. 83 and 84, the number of processes, particularlythe dendritic processes, is much greater in the cortical cellsof the higher animals; or, to put this fact in another way, thenumber of cells in the cortex of the higher animals is much lessfor an area of the same size than in lower animals. The amountof in-between substance or the richness of the network of processes
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Fig. 83.-—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; 6, commencing dendrites; c, dendritesfurther developed; d, first appearance of collateral branches; e, further development ofcollaterals and dendrites.—(From Ramon y Cajal.) is increased. This anatomical fact would indicate that the greatermental activity in the higher animals is dependent, in part, uponthe richer interconnection of the nerve cells, or, expressed physio-logically, our mental processes are characterized by their morenumerous and complex associations. A visual or auditory stim-ulus that, in the frog, for instance, may call forth a comparativelysimple motor response, may in man, on account of the numerousassociations with the memory records of past experiences, lead

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