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CHAPTER XXI. 



THE SYMPATHETIC NERVE. ITS ANATOMY AND FUNCTIONS. 



UNDER the title of Sympathetic nerve is comprehended a great 

 subdivision of the nervous system, which presents certain peculiar- 

 ities of structure and of distribution, whereby it is strikingly con- 

 trasted with the strictly cerebro-spinal nerves. 



It consists of an uninterrupted chain of ganglia, extending on 

 each side of the vertebral column, from the first cervical vertebra 

 down to the coccyx, and moreover extending upwards beside the 

 cranial vertebrse, and occupying spaces between the bones of the 

 cranium and those of the face. 



The ganglia are on the whole rather less numerous than the 

 vertebrse : in the dorsal region there is generally a ganglion for each 

 vertebra. The continuity of the chain is preserved by cords of 

 communication which pass from one to the other : sometimes two 

 ganglia are, as it were, fused together; the chains of opposite sides 

 communicate with each other at various parts in the plexuses of nerves 

 which originate from them, and, in front of the coccyx, through a 

 single ganglion (ganglion impar), which is situate in front of that 

 bone; whether they communicate at the cephalic extremity, or 

 not, is uncertain. Hibes has described a ganglion impar upon the 

 anterior communicating artery of the circle of Willis, similar to 

 that on the coccyx, and other anatomists regard the pituitary body 

 in the sella Turcica as a ganglion of this description, a common 

 point of union for the right and left sympathetic chains at their 

 cranial extremities. 



The sympathetic nerve has very much the same general arrangement in mam- 

 malia and birds as in man. In the former the cervical portion is closely associ- 

 ated with the vagus nerve by a sheath of areolar tissue, but without inter- 

 change of fibres, excepting at its upper portion. In birds the cervical portion 

 exists only in the canal formed by the foramina of the transverse processes of the 

 vertebrce. In the batrachian reptiles the sympathetic is disposed as in mam- 

 malia. In the chelonian reptiles its ganglia are few and the lateral cords small. 

 In serpents, it appears to want the distinct ganglia which exist in other animals ; 

 it is, however, continued down the spine on each side, having frequent commu- 

 nications with the vagus. Numerous plexuses occur in its course. In the larger 

 osseous fishes the sympathetic is sufficiently distinct, as in the cod; it is also 

 present in the ray ; in both, but especially the latter, it is the abdominal por- 



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