THE NEKVES, 



E V 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 do^s nob 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 cerebro- 

 spinal axis, which they leave as constituents of the roots of certain of the cerebro- 

 spinal 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 cerebrates), 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 Saemmering 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 tog-ether 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 



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