THE THOEAX. 



463 



they lodge the superior border of the pulmonary lobes. The middle 

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

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

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

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

 sympathetic nerve. 



The inferior plane, much shorter than the preceding, is, like it, narrower 

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

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

 it gives attachment to the fibrous sac containing the heart. 



. 234. 



THE PECTORAL CAVITY AND MEDIASTINUM, WITH THE COURSE OP THE TRACHEA 

 AND (ESOPHAGUS. 



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

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

 (Esophagus. 



The lateral planes, more extensive than the other two, are concave in 

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

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

 lung. 



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

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

 and by the last rib. In it we see the three openings which traverse the 

 diaphragmatic septum. 



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

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

 and which is partly obstructed by an enormous collection of lymphatic 

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

 and carotid arteries, the anterior vena cava, and the pneumogastric, great 

 sympathetic, inferior laryngeal, and diaphragmatic nerves. 



