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) (14782310602).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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ry clear Fig 10—Branch of a nerve distributed to one i -i -• •, 3 of the muscles of the eye of a sparrow, included substance, and a transparent tubular sheath. The double line or contourof either side being the optical expression of the inner andouter wall of this tube. Other observers admit a more com-pound structure, and some have even spoken of a ciliary epi-thelium, lining the inner aspect of the sheath. (§ 81. These primary tubes or fibres of the peripheralnerves are similar, with very slight modifications, in everypart of the nervous system. It is necessary, however, to ex-cept from this general rule the first and second cerebralnerves. In the auditory nerve the fibres are somewhat moredelicate than elsewhere. They also very commonly appearrather finer than wont where they traverse ganglions. Theyappear to be distributed over the periphery of the body, with-out, in any instance, anastomosing. They have a central anda peripheral termination. With reference to the first, or
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NERVOUS SYSTEM AND GENERAL SENSATION. where they enter the brain or spinal cord as roots of nerves,they pass immediately into the white medullary fibres, or cen-tral parts, and at the same time become by one-half, or eventwo-thirds, smaller. The primary fibres of the brain andspinal cord, as well as those of the olfactory and auditorynerves, are in some cases so delicate, that they measure butthe 1 -1000th of a line in diameter : frequently, however, theyare thicker, from the 1 -400th to the 1-500th of a line indiameter. These fibrils, of different dimensions, are constantlyobserved running over, and under, and near to one another. (Figs. 9, 10, B, and11, C.) Examined inthe most recent statepossible, they are, forthe major part, cy-lindrical, but in partalso knotty or vari-cose, inasmuch asthey exhibit little ovalor rounded enlarge-ments in their course. (Figs. 9,B, H,A,B.)It is doubtful whe-ther or not this vari-cose state is acciden-tal only, or is reallypeculiar to certainprimary f

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