THE BACK. 195 



and sends brandies backwards to supply tlie abdominal 

 muscles. The common carotid is situated below the trachea 

 in the anterior -psivt of the thorax, between the two first 

 ribs. It arises from the right arteria innominata, and ter- 

 minates in bifurcating to form the right and left carotid 

 arteries. 



The thoracic duct after passing through hiatus aorticus 

 runs forwards situated between vena azygos on the right 

 and posterior aorta on the left. Opposite, about the sixth 

 dorsal vertebra, it swerves to the left side and passes towards 

 the anterior opening of the thorax to terminate in the left 

 jugular or the left axillary vein. Its walls are very thin, so 

 that its course is demonstrable but with difficulty. Almost 

 in apposition with the inner surface of the first rib we may 

 find the inferior cervical ganglion, to which the sympa- 

 thetic cord running down the neck passes, after presenting 

 a little below and in front a small nodular enlargement, the 

 middle cervical ganglion. The inferior cervical ganglion 

 also receives a band of nerve-fibres coming from the fora- 

 mina in the transverse processes of the cervical vertebrse, 

 made uj) of fibres derived from the cervical nerves while 

 emerging through the intervertebral gaps in the neck. 

 From this ganglion backwards extends the gangliated cord, 

 running first against the lateral part of the longus colli 

 muscle, then at the suj)ero-lateral part of the thorax against 

 the heads of the ribs, having a ganglion opposite each 

 vertebra and being visible through the pleura costalis, by 

 which only it is covered. Each ganglion receives fibres 

 through the nearest intervertebral gap from the spinal cord, 

 and sends fibres to the neighbouring intercostal nerves 

 From the thirteen or fourteen posterior ganglia fibres 

 are given off which combine to form the greater splanchnic 

 nerve, with difficulty separable from the gangliated cord as 

 it runs backwards, and passes above the diaphragm with 

 the psoas muscles to reach the semilunar ganglion in the 

 antero-superior part of the abdomen, some of its fibres run- 

 ning directly to the kidney. The lesser splanchnic nerve 

 arises from the two or three posterior dorsal ganglia, and 

 accompanies the greater nerve, terminating in a similar 

 manner. The inferior ganglion gives off fibres which run 

 downwards to assist the pneumogastric in forming the car- 

 diac i^lexus at the base of the heart, and the i^ulmonary at the 

 root of the lungs. These plexuses have communication with 



