TIIK nnn;.\\. 



468 



they lodgo tho superior border of the pulmonary lobes. The middlo 

 projection, or ridge, is comprised between these two lobes. Covered in front 

 by the posterior extremity of the lougus colli, this ridge responds, for the 

 remainder of its extent, to the posterior aorta, the thoracic canal, and tho 

 vena azygos; on its sides are seen the subdorsal branches of the great 

 sympathetic nerve. 



Tho inferior plane, much shorter than tho preceding, is, like it, narrower 

 iu front than behind ; it has for a base the superior face of tho sternum, 

 the sternal cartilages, and the triangularis sterui muscle. Posteriorly, 

 it gives attachment to the fibrous sac containing tho heart. 



Fig. 234. 



AtLrl L, 



I 111-; PECTORAL CAVITY AND MEDIASTINUM, WITH Till; COURSE OF THE TRACHEA 

 AND (ESOPHAGUS. 



A, Anterior mediastinum ; 11, Posterior mediastinum ; c, The heart and pericar- 

 dium in the middle part of the mediastinum; D, Diaphragm; E, Trachea; F, 



Tho lateral planes, more extensive than the other two, ore concavo in 

 both their diameters. Formed by tho internal face of tho ribs and tho 

 deep intercostal muscles, they are in contact with tho external face of tho 

 tang. 



The base, or posterior plane, formed by tho convex face of tho diaphragm, 

 is circumscribed on its exterior contour by tho circle of asternal cartilages, 

 ami by tho lost rib. In it we see tho throe openings which traverse tho 

 diaphragmatic septum. 



Tho summit, or entrance of the thorax, is an oval opening, elongated 

 vertically, comprised between tho two first ribs and the longus colli muscle, 

 and which is partly obstructed by an enormous collection of lymphatic 

 glands; through this opening passes tho trachea, oesophagus, tho axillary 

 and carotid arteries, tho anterior vena cava, and the pnoumogastrio, great 

 <Yinpatlietu-. inferior laryugeal, and diaphragmatic nerves. 



