CHAPTER XXIV. 

 THE AUTONOMIC NERVE SYSTEM. 



The autonomic nerve system consists of i, the sympathetic ganglia and 

 their branching nerve-fibers, and 2, fine medullated nerve-fibers contained 

 in the trunks of some of the cranial and some of the spinal nerves, which 

 serve to bring the nerve-cells in which they arise into relation with the sym- 

 pathetic ganglia. The fine-medullated nerve-fibers arising in cells in dif- 

 ferent parts of the central nerve system and passing outward in the trunks 

 of various nerves are termed from their relation to the sympathetic ganglia, 

 pre-ganglionic fibers; the non-medullated fibers arising in and emerging from 

 the sympathetic ganglia are termed post-ganglionic fibers. 



This system of nerves is distributed almost exclusively to the epithelium 

 of secretor organs and to the non-striated muscle-fibers in the walls of the 

 blood-vessels, including the striated fibers of the heart, and the non-striated 

 muscle-fibers in the walls of the hollow viscera. 



Inasmuch as this system of nerves is supposed to be in a measure inde- 

 pendent, self-regulative, or autonomous in its activity, but at the same time 

 under the control of a higher power it has received the name of the auto- 

 nomic nerve system. (Langley.) 



It will be found convenient to consider first the sympathetic ganglia and 

 the distribution of their post-ganglionic fibers, and second, the origin, course 

 and distribution of the pre-ganglionic fibers. The sympathetic ganglia may 

 for convenience of description be divided into three groups: viz., the vertebral 

 or lateral, the pre-vertebral or collateral, and the peripheral or terminal. 



The vertebral ganglia are arranged in the form of chains, one on each 

 side of the vertebral column. The number of ganglia in the chain varies in 

 animals of different and in animals of the same species. In man the number 

 varies from 20 to 22. Each chain may be divided into a cervical, a thoracic, 

 a lumbar, a sacral, and a coccygeal portion. The cervical portion is usually 

 described as consisting of three ganglia a superior, a middle, and an inferior. 

 This statement is open to question, however, as the middle one is frequently 

 absent and the inferior one is regarded by some anatomists as belonging to 

 the pre-vertebral series. The thoracic portion consists of ten or twelve 

 ganglia, the lumbar and sacral portions of four each and the coccygeal 

 portion of one, the so-called ganglion impar. 



The pre-vertebral ganglia are also united in the form of a chain situated 

 in the abdominal cavity. The ganglia constituting this chain are known as 

 the semilunar, the renal, the superior and inferior mesenteric, and 

 hypogastric, or selvic. 



The periphearl ganglia are in more or less close relation with the tissues 

 and organs in different parts of the body. As members of this group 

 may be mentioned the ciliary or ophthalmic, the spheno-palatine, the otic, 

 the submaxillary and the sublingual ganglia; the ganglia in walls of the heart, 

 the respiratory organs, the stomach and intestines, the bladder, etc. 



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