350 A MANUAL OF ANA TO MY. 



receives the six left, lower intercostal veins, the left medi- 

 astinal, and cesophageal veins (lower). 



(3) The left superior azygos azygos tertius (often ab- 

 sent). When present, receives the fourth to the seventh 

 or eighth intercostal veins inclusive, some mediastinal, and 

 the left bronchial veins. It communicates with the left 

 superior intercostal vein above, and empties into the azygos 

 major below. 



(4) The right superior intercostal vein is formed by the 

 second, third, and sometimes fourth right intercostal veins, 

 and empties into the azygos major as it arches to terminate 

 in the vena cava superior. 



The first right intercostal vein empties into the innomi- 

 nate or vertebral vein. 



(5) The left superior intercostal, formed by the first two 

 or three left intercostal veins, opens into the innominate 

 (left). It communicates below with the left superior 

 azygos. 



The Intercostal Nerves. Fig. 74. 



These are the anterior branches of the twelve dorsal 

 nerves which supply the walls of the chest and abdomen. 

 The first intercostal nerve sends four-fifths of its fibres to 

 join the brachial plexus and the remaining fifth takes a 

 course similar to the other intercostal nerves. 



The intercostal nerves from the second to the sixth in- 

 clusive terminate anteriorly as the anterior cutaneous nerves 

 of the thorax. See page 266. The next nerves below, 

 from the seventh to the eleventh inclusive, course between 

 the transversalis and internal oblique muscles, and termi- 

 nate in front as the anterior cutaneous nerves of the abdo- 

 men. The course of the twelfth is given with the lumbar 

 plexus. All these nerves give off lateral cutaneous 



