EDWARD ALBERT SCHÄFER, F.R.S.

PROFESSOR OF PHYSIOLOGY AND HISTOLOGY IN UNIVERSITY COLLEGE, LONDON,

AND

GEORGE DANCER THANE,

PROFESSOR OF ANATOMY IN UNIVERSITY COLLEGE, LONDON.

IN THREE VOLUMES.

VOL. III.-PART IL

THE NERVES.

BY PROFESSOR THANE.

ILLUSTRATED BY 102 ENGRAVINGS.

REPRINTED FROM THE

Tenth Edition.

LONGMANS, GREEN, AND CO.

39 PATERNOSTER ROW, LONDON

NEW YORK AND BOMBAY

1897

BOSTON MEDICAL LIBRARY

IN THE

FRANCIS A. COUNTWAY
LIBRARY OF MEDICINE

BRADBURY, AGNEW, & CO. LD., PRINTERS,

LONDON AND TONBRIDGE.

THE NERVES.

By G. D. THANE.

In this section is comprised the descriptive anatomy of the cerebro-spinal and sympathetic nerves, and their ganglia. Together with these the peripheral division of the nervous system also includes the organs of the external senses, which will be described in the following section. The minute structure of the nerves and their mode of ending in the several tissues and organs of the body are discussed in the sections General Anatomy and Splanchnology.

The separation of the sympathetic from the cerebro-spinal nerves is convenient for purposes of description, but does not indicate a difference of origin or an anatomical independence of the two systems, since the fibres composing the sympathetic are connected centrally, either directly or indirectly, with the cerebrospinal axis, which they leave as constituents of the roots of certain of the cerebrospinal nerves. Moreover, the division cannot in all cases be strictly maintained, for some of the ganglia (ciliary, spheno-palatine, otic, and submaxillary), which are described in connection with the cranial nerves to which they are attached, have a close affinity with those of the sympathetic system, while on the other hand many of the terminal plexuses distributed to the viscera, and generally regarded as parts of the sympathetic system, are composed in large part of fibres which pass into them directly from cerebro-spinal nerves without traversing the cord of the sympathetic.

THE CEREBRO-SPINAL NERVES.

The nerves springing directly from the great cerebro-spinal centre constitute a series of symmetrical pairs, of which twelve issue from the cranium through different apertures in its base, and are thence named cranial. The next following nerve passes out between the occipital bone and the atlas, and the remaining thirty nerves all issue below the successive segments of the vertebral column. The first is sometimes distinguished by the name of suboccipital, but to the whole series of thirty-one nerves the name of spinal will be here given.

CRANIAL NERVES.

The cranial nerves (nervi cerebrales), besides being distinguished by numbers in the order of their passage through the dura mater lining the cranium, have likewise received other names, according to the place or mode of their distribution, or their functions.

The number of the cranial nerves is now universally stated as twelve, following the enumeration which was proposed by Sommering in 1778, but has only recently been adopted in this country. Previously they were reckoned as nine pairs, in accordance with the classification of Willis (1664), in which the facial and auditory together compose the seventh pair, while the glosso-pharyngeal, pneumo-gastric, and spinal accessory are included in the eighth. Willis also looked upon the suboccipital as a cranial nerve, and thus counted ten

VOL. III. PT. 2.

P