THORAX 



body of the ninth thoracic vertebra. 1 The bodies of the 

 thoracic vertebrae project forwards into the cavity of the 

 thorax, and greatly diminish its antero-posterior diameter 

 in the median plane; but the backward sweep of the 

 posterior portions of the ribs produces a deep hollow on 

 each side of the vertebral column, for the reception of the 

 most massive part of the corresponding lung (Fig. 5). 



The superior aperture, or inlet of the thorax, is a narrow 

 opening which is bounded by the first thoracic vertebra, the 

 first pair of costal arches, and the manubrium sterni (Fig. i). 

 The plane of the superior aperture is very oblique ; it slopes 

 from the first thoracic vertebra forwards and downwards. 



Right vagus nerve 



Right 

 subclavian artery 



Right 

 innominate vein 



Innominate 

 artery 



Trachea 



(Esophagus Left subclavian artery 



Sulcus subclavius 



Left vagus nerve 



Left 



common 



carotid 



Left 



innominate 

 vein 



FIG. i. Cervical Domes of the Pleural Sacs, and parts in relation to them. 



Through the aperture the apices of the lungs project upwards 

 into the root of the neck, and, between them, the followir, ; 

 structures either enter or leave the thorax : the trachea, the 

 oesophagus, the vagi, the phrenic nerves, the left recurrent 

 nerve, the ganglionated sympathetic trunks, the thoracic duct, 

 and the great arteries and veins which carry blood to and 

 from the head and neck and the upper limbs. 



The base or inferior aperture of the thorax is very wide, 

 and is sometimes called the outlet. Anteriorly, it is bounded 

 by the xiphoid process, and, posteriorly, by the twelfth thoracic 

 vertebra. Between those points the lower margin of the 

 thorax presents a curved outline. Starting from the sternum, 

 it passes downwards, laterally, and backwards, as far as the 



1 This statement refers to average conditions. Not uncommonly the 

 lower end of the body of the sternum is at the level of the tenth thoracic 

 vertebra (Fig. 28). 



