40 THORAX 



between the ganglia. It passes downwards, on the bodies of 

 the vertebrae, enters the abdomen by piercing the crus of the 

 diaphragm, and ends in the coeliac ganglion of the same side. 



Opposite the last thoracic vertebra there is frequently a small ganglion 

 upon the greater splanchnic nerve, or connected with it ; from that ganglion 

 branches are distributed to the aorta, where they communicate with their 

 fellows of the opposite side. 



Nervus Splanchnicus Minor. The lesser splanchnic nerve 

 arises by two roots either from the ninth and tenth, or from 

 the tenth and eleventh ganglia. It also pierces the crus of 

 the diaphragm and ends in the coeliac ganglion. 



Nervus Splanchnicus Imus. The lowest splanchnic nerve is 

 a minute branch which springs from the last thoracic ganglion. 

 It is frequently absent, but when it is present it pierces the 

 crus of the diaphragm and ends in the renal plexus. 



Dissection. When the study of the thoracic portion of the 

 sympathetic trunk and its branches is completed, the posterior 

 parts of the intercostal spaces should be cleaned and examined. 

 The internal intercostal muscles will be seen passing as far 

 medially as the angles of the ribs. In some cases fibres with 

 the same direction as those of the internal intercostal muscles 

 will be found descending from one rib to the second or third 

 below, across the pleural surfaces of the intervening ribs. Such 

 fibres constitute the subcostal muscles, which are very variably 

 developed in different subjects. Sometimes they form an almost 

 complete lining for the posterior part of the thoracic wall, and 

 in other cases they are represented by a few scattered fibres, or 

 they are entirely absent. 



After the posterior parts of the intercostal spaces have been 

 cleaned, remove, on both sides, the strip of pleura which was 

 left over the phrenic nerve ; then clean the nerve and the accom- 

 panying vessels, but do not displace the nerve. If the nerve 

 is accidentally displaced fix it back in position by means of a few 

 stitches, attaching the right nerve to the right innominate vein, 

 the superior vena cava, the pericardium, and the inferior vena 

 cava, along which it runs, and the left nerve to the left common 

 carotid artery, the arch of the aorta, and the pericardium. 



After the phrenic nerve has been cleaned the dissector on 

 the left side should follow the recurrent branch of the vagus 

 below the arch of the aorta, and at the lower border of the arch, 

 immediately medial and anterior to the recurrent nerve, he should 

 find a fibrous cord, called the ligamentum arteriosum, which 

 connects the inferior border of the arch with the commencement 

 of the left pulmonary artery. The ligament must be carefully 

 cleaned and preserved, but the superficial cardiac plexus which 

 lies medial to it must not be interfered with at present. When 

 the dissection outlined above is completed the dissectors should 

 study the vena azygos, the left superior intercostal vein, the 

 phrenic nerves and their accompanying vessels, and the posterior 

 intercostal membranes. 



