54 TOPOGRAPHICAL ANATOMY OF THE 



costal arteries; or the truuk may be absent, in which case the bronchial 

 and oesopliageal arteries rise separately ftoni the aorta or from the 

 intercostal artery. 



The bronchial artery (a. bronchialis) runs in a vertical direction 

 between the aorta and the oesophagus to the bifurcation of the trachea, 

 where it divides into riglit and left branches for the nutritive supply of 

 the right and left lungs respectively. Some twigs are furnished to the 

 trachea, oesophagus, pleura and the bronchial lymph glands. 



The wsojiJiafjeal artery (a. oesophagea) is the smaller of the two 

 branches of the broncho-oesophageal trunk. It runs along the dorsal 

 border of the oesophagus to the diaphragm and anastomoses with the 

 (oesophageal ramus of the left gastric artery. Small branches are 

 distributed to the oesophagus, caudal mediastinal lymph glands and the 

 pleura ; and two or three branches pass between the two layers of 

 the pulmonary ligament to the lungs, where they ramify underneath 

 the pleura. 



(2) Arterice inter costales. — The first four (possibly five) intercostal 

 arteries have been described in connection with the deep cervical and 

 supreme intercostal arteries, from which they arise. The remaining 

 thirteen (or twelve), which may be conveniently distinguished as the 

 aortic intercostals, spring from the dorsal surface of the aorta in 

 pairs ; but the fifth and sixth not uncommonly leave the aorta as 

 a common stem. 



Each intercostal artery crosses the body of a thoracic vertebra to 

 reach the vertebral end of an intercostal space where it divides into 

 dorsal and ventral rami. A description of these has already been 

 given (page 7). 



About the origins of the intercostal arteries small lymph glands 

 (lymphoglandulfe intercostales) should be sought. 



(3) Arterice phrenicce craniales. — Two small cranial phrenic 

 arteries leave the ventral face of the aorta as it is passing through the 

 hiatus aorticus of the diaphragm, or arise from the aorta in common 

 with an intercostal artery. They are distributed to the crura of the 

 diaphragm. 



V. AzYGOS.— The vena azygos begins by the union of the first pair 

 of lumbar veins. Entering the thorax to the right of the aorta, it 

 passes along the vertebral bodies to the right of the median plane as 

 far as the sixth thoracic vertebra. Then the vein curves towards the 

 heart, and finally opens into the cranial vena cava just as this is entering 

 the right atrium, or it may possibly enter the atrium directly. To the 

 left the vein is in contact with the thoracic duct and the aorta. Towards 

 its termination it crosses the right face of the oesophagus and trachea. 



