1116 



THE ORGANS OF VOICE AND RESPIRATION. 



vena cava and the innominate veins, and the left superior intercostal vein ; the 

 pneumogastric, cardiac, phrenic, and left recurrent laryngeal nerves ; the trachea, 

 oesophagus, and thoracic duct ; the remains of the thymus gland and lymphatics. 

 The anterior mediastinum is bounded in front by the sternum, on each side by 

 the pleura, and behind by the pericardium. Owing to the oblique position of the 



Left Inom- Left Carotid Thymus 

 inate Vein. Artery. Gland. 



Pneumogastric 

 Nerve. 



Pneumogastric 

 Nerve. 

 \ 



Internal Mammary 

 Artery. 



Right Innom- 

 - inate Vein. 

 1st Rib. 



Trachea. 



Vertebral 

 Artery..- 

 Left Sublcavian, 

 Artery. 



(Esophagus.-'' 



2nd Rib. 



V 



3rd Rib. 



FIG. 709. Transverse section through the upper margin of the third dorsal vertebra. (Braune.) 



heart toward the left side, this space is not parallel with the sternum, but directed 

 obliquely from above downward and to the left of the median line ; it is broad 

 below, narrow above, very narrow opposite the first segment of the gladiolus of the 

 sternum, the contiguous surfaces of the two pleurae being occasionally united over a 

 small space. The anterior mediastinum contains the origins of the Triangularis 

 sterni muscles, and a quantity of loose areolar tissue in which some lymphatic 

 vessels are found ascending from the convex surface of the liver, and two or three 

 lymphatic glands (anterior mediastinal glands). 



The middle mediastinum is the broadest part of the interpleural space. It 

 contains the heart enclosed in the pericardium, the ascending aorta, the lower 

 half of the superior vena cava, with the vena azygos major opening into it, the 

 bifurcation of the trachea and the two bronchi, the pulmonary artery dividing into 

 its two branches and the right and left pulmonary veins, the phrenic nerves, and 

 some bronchial lymphatic glands. 



The posterior mediastinum is an irregular triangular space running parallel 

 with the vertebral column ; it is bounded in front by the pericardium and roots of 

 the lungs, behind by the vertebral column from the lower border of the fourth 

 dorsal vertebra, and on either side by the pleura. It contains the descend- 

 ing thoracic aorta, the greater and lesser azygos veins, the pneumogastric and 

 splanchnic nerves, the oesophagus, thoracic duct, and some lymphatic glands. 



THE LUNGS. 



The Lungs are the essential organs of respiration ; they are two in number, 

 placed one on each side of the chest, separated from each other by the heart and 



