File:A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine (1890) (14740555936).jpg

Identifier: textbookofcompar00mill (find matches)
Title: A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine
Year: 1890 (1890s)
Authors: Mills, Wesley, 1847-1915
Subjects: Physiology, Comparative
Publisher: New York, London, D. Appleton and company
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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st whollyreferable to the surface of the body. Without some knowledge of the mode of development oftbe encephalon, it is scarcely possible to appreciate that risinggrade of complexity met with as we pass from lower to highergroups of animals, especially noticeable in vertebrates ; nor isit possible to recognize fully the evidence found in the nervoussystem for the doctrine that higher are derived from lowerforms by a process of evolution. Evolution.—The same law applies to the nervous system asto other parts of the organism, viz., that tbe individual devel-opment (ontogeny) is a synoptical representation, in a generalway. of the development of the group (phylogeny). A com-parison of the development of even mans brain reveals the factthat, in its earliest stage, it is scarcely, if at all, distinguishablefrom that of any of the lower vertebrates. There is a periodwhen even this, the most convoluted of all brains, is as smoothand devoid of gyri as the brain of a frog. The extierne com-
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PlG. 367.—A. brain of aye-aye (Lemur); B. of marmoset; C. of squirrel monkey (Cal-lithri.c); D, of macaque monkey; E, of gibbon; F, of a fifth-month human foetus(after (>wen i. Although naturalists are agreed that tbe monkey.-, apes, and lemursare related, considerable differences are to be observed in their brains. These fig-ures also illustrate the remark made after those following. plexity of the human brain is referable to excessive growth ofcertain parts, crowding and alteration of shape, owing to theinfluence of its bony case, its membranes, etc. 512 COMPARATIVE PHYSIOLOGY. It is evident, from an inspection of the cranial cavities ofthose enormous fossil forms that preceded the higher verte-brates, that their brains, in proportion to their bodies, werevery small, so that any variation in the direction of increasein the encephalon—especially the cerebrum—must have giventhe creatures, the subject of such variation, a decided advan-tage in the struggle for existence, and o

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