File:Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct - for the use of schools and colleges (1870) (14596020998).jpg

Identifier: outlinesofcompar00agas (find matches)
Title: Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges
Year: 1870 (1870s)
Authors: Agassiz, Louis, 1807-1873 Gould, Augustus A. (Augustus Addison), 1805-1866 Wright, Thomas, 1809-1884
Subjects: Physiology, Comparative Zoology
Publisher: London : Bell & Daldy
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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KERYOUS SYSTEM AND GENERAL SENSATION. 33 terised by the double contour, than those of the peripheralfibres. In the central fibres, too, the sheath and contents appearto be far more intimately connected ; in many cases they arecompletely inseparable, so that the contrast as betwixt sheathand contents disappears. These delicate primary fibrils ofthe central masses run in such a variety of ways, crossing andinterlacing, and forming such a tangled skein, that it isimpossible to follow them to the roots of the nerves, or towardsthe periphery of the brain and cord, and so to make certainthat they never anastomose. To all appearance, however, they
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Fig. 12.—A small portion of the terminal plexus of primary fibres of theauditory nerve in the auditory sac of the pike (Esox lucius.) 34 NERVOUS SYSTEM AND GENERAL SENSATION. never divide ; and they seem no more to run into one another,or to communicate by anastomoses here, than they do in theperipheral parts of the body. But these fine primary fibresof the central parts enlarge conspicuously and immediatelyat the entrances of the different nerves into the brain andspinal cord. TERMINATION Or THE PRIMARY FIBRES. (§ 82. A very important question, which naturally presentsitself in connexion with the primary fibrils, is this : how dothey end? Although generally traced with difficulty, theperipheral terminations of the nervous fibrils are still muchmore easily demonstrated than those of the centres. Unitedinto bundles, and surrounded with cellulo-membranous sheaths(neurilema), the primary fibres penetrate all the organs nearly to their peripheral confines, to wherethey are covered with

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