SECTION XVIII 



THE VISCERAL OR AUTONOMIC NERVOUS 



SYSTEM 



IN the medulla oblongata it is easy to differentiate the central 

 grey matter connected with the peripheral nerves into two categories, 

 viz. splanchnic and somatic. Each of these two sets of nerves 

 possesses both afferent and efferent fibres. Gaskell has suggested 

 that the same arrangement would hold for any typical segmental 

 nerve, which would therefore have four roots, viz. two somatic 

 the motor and sensory roots distributed to the skin and skeletal 

 muscles and two splanchnic roots, also motor and sensory, and 

 composed of small fibres distributed to the viscera or structures 

 which are visceral in origin (e.g. developed from the branchial arches). 

 In the medulla the somatic efferent fibres, such as the sixth and 

 twelfth nerves, arise from the column of large cells lying in the floor 

 of the fourth ventricle close to the middle line. The splanchnic 

 fibres, e.g. those of the facial and vago-glossopharyngeal nerves, 

 arise from a column of cells the nucleus ambiguus and facial nucleus, 

 lying more laterally and deeper, below the. surface of the ventricle. 

 The motor root of the fifth would also belong to the same system. 

 In the spinal cord the visceral fibres arise in the cells of the lateral 

 horn, i.e. from a situation corresponding to the splanchnic motor 

 nuclei of the pons and medulla. Whereas, however, the splanchnic 

 afferent nerves, such as the glossopharyngeal ; and perhaps the 

 sensory nucleus of the fifth, form a well-marked splanchnic system 

 of nuclei in the medulla, in the cord the afferent fibres from the viscera 

 pass in with the other afferent somatic fibres, and their immediate 

 connections in the cord are as yet unknown. 



The autonomic system of nerves includes the sympathetic system 

 (properly so called) and some of the cranial and sacral nerves. 

 The sympathetic system (Fig. 235) is composed of a chain of 

 ganglia lying each side of the vertebral column, there being as a 

 rule one ganglion to each spinal nerve-root. In the cervical region 

 these ganglia are condensed into two, the superior and inferior cervical 

 ganglia, united by the cervical sympathetic trunk ; and the upper 



three or four thoracic ganglia on each side are condensed to form the 



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