SECTION XIX 

 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-glosso- 

 pharyngeal nerves, arise from a column of cells the nucleus ambiguos 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 sym- 

 pathetic system (Fig. 237) 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 sympa- 

 thetic trunk ; and the upper three or four thoracic ganglia on each side are 

 condensed to form the ' stellate ' ganglion. At the bottom of the chain 

 there is only one coccygeal ganglion for the coccygeal vertebrae. 



In the abdomen is a second system of ganglia, in special connection 

 with the abdominal viscera, lying in front of the aorta and surrounding the 

 origins of the large arteries to the alimentary canal. These are the semilunar 

 or solar ganglia, the superior mesenteric and the inferior mesenteric ganglia. 



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