172 THE HUMAN BODY. 



nerves often receive branches from neighboring cranial or 

 spinal nerves, so that very soon after it leaves the brain 

 hardly any one remains free from fibres derived from other 

 trunks except the olfactory, optic, and auditory nerves. 

 This often makes it difficult to say from where the nerves 

 of a special part have come; for example, the nerve-fibres 

 going to the submaxillary salivary gland from the trigemi- 

 nal leave the brain first in the facial and only afterwards 

 enter the fifth; and many of the fibres going apparently 

 from the pneumogastric to the heart come originally from 

 the spinal accessory. 



The Sympathetic System. The ganglia which form 

 the main centres of the sympathetic nervous system lie in 

 two rows (s, Fig. 2, and sy, Fig. 3), one on either side of 

 the bodies of the vertebrae. Each ganglion is united by a 

 nerve-trunk with the one in front of it, and so two great 

 chains are formed reaching from the base of the skull to 

 the coccyx. In the trunk "region ,these chains lie in the 

 ventral cavity, their relative position in which is indicated 

 by the dots sy in the diagrammatic transverse section re- 

 presented on p. 7 in Fig. 3. The ganglia on these chains are 

 forty-nine in number, viz., twenty-four pairs, and a single 

 one in front of the coccyx in which both chains terminate. 

 They are named from the regions of the vertebral column 

 near which they lie; there being three cervical, twelve 

 dorsal, four lumbar, and five sacral pairs. 



Each sympathetic ganglion is united by communicating 

 branches with the neighboring spinal nerves, and near the 

 skull with various cranial nerves also; while from the gan- 

 glia and their uniting cords arise numerous trunks, many 

 of which, in the thoracic and abdominal cavities, form 

 plexuses, from which in turn nerves are given off to the 

 viscera. These plexuses frequently possess numerous small 

 ganglia of their own; two of the most important are the 

 cardiac plexus which lies on the dorsal side of the heart, 

 and the solar plexus which lies in the abdominal cavity and 

 supplies nerves to the stomach, liver, kidneys, and intes- 

 tines. Many of the sympathetic nerves finally end in the 

 walls of the blood-vessels of various organs. To the naked 



