THORACIC CAVITY 39 



cervical portion and below with the abdominal portion. It 

 has the appearance of a knotted cord. The knots are 

 ganglia, which consist of nerve cells and fibres. The inter- 

 mediate parts of the trunk consist of nerve fibres alone. 

 There are usually eleven ganglia, and, as a rule, each 

 ganglion lies opposite the head of a rib, but the first is 

 opposite the medial end of the first intercostal space, or 

 anterior to the neck of the first rib ; and, as the trunk 

 inclines forwards below, one or two of the lower ganglia 

 lie on the bodies of the lower thoracic vertebrae. 



Branches. The branches of each sympathetic trunk may 

 be divided into two groups (i) Lateral; (2) Medial. 



(1) Lateral Branches. From each ganglion two branches 

 pass laterally into the adjacent intercostal space, where they 

 join the corresponding intercostal nerve. One of the 

 branches, called the white root of the ganglion, contains 

 medullated fibres which are passing from the medulla spinalis 

 (O.T. spinal cord) through the intercostal nerve to the 

 ganglion. The other, the grey root, consists of non-medullated 

 fibres which are passing from the cells of the ganglion to the 

 intercostal nerve. Some of the fibres of the grey root are 

 distributed with the branches of the intercostal nerve, and 

 others run medially, in the intercostal nerve, to the spinal 

 nerve trunk, whence some are distributed by the posterior 

 ramus and others pass more medially to the membranes 

 of the medulla spinalis. 



(2) Medial Branches. (a) Pulmonary; (ft) Aortic; (c) 

 Splanchnic. (a) The pulmonary branches arise from the 

 second, third, and fourth ganglia. They run forwards to the 

 posterior surface of the root of the lung, where they com- 

 municate with branches of the vagus, and assist in forming 

 the posterior pulmonary plexus, (b) The aortic branches are 

 fine filaments which arise from the upper five ganglia and pass 

 to the coats of the aorta ; the dissector will rarely be able to 

 trace them in an ordinary dissection, (c) The splanchnic 

 branches arise from the sixth to the last ganglion, and they run 

 together to form three distinct nerves the greater, the lesser, 

 and the lowest splanchnic nerves, which are all destined for 

 the abdominal viscera. 



Nervus Splanchnicus Major. The greater splanchnic nerve 

 is formed by the union of four or five roots derived from the 

 sixth to the tenth ganglia, or from the portions of the trunk 



