ANATOMY AND PHYSIOLOGY. 



ANTERIOR MEDIASTINUM, 



A triangular cavity formed by tearing through the cellular tissue, 

 which connects the right and left pleura behind the sternum ; the 

 base is formed by the sternum, the sides by the separated pleura, 

 and the apex corresponds to the anterior surface of the peri- 

 cardium, where the pleurae separate to enclose this bag. Thus 

 formed, it contains the origins of the sterno-hyoid and sterno- 

 thyroid muscles, branches of the descendens noni nerve, the remains 

 of the thymus gland, lymphatic glands and a^orbents, the mam- 

 mary vessels, the triangulare sterni muscles, and loose cellular 

 tissue. 



MIDDLE MEDIASTINUM 



Is of an oval shape, and is formed by the reflection of the pleura 

 upon the sides of the pericardium ; it consequently contains this 

 bag and its contents. 



POSTERIOR MEDIASTINUM 



Is formed by the reflection of the pleurae upon the sides of the 

 bodies of the vertebrae ; it is of a triangular form, the apex anterior 

 corresponding to the posterior surface of the pericardium, the sides 

 formad by the pleurae, and the base represented by the anterior sur- 

 faces of the bodies of the vertebrae ; it extends from the third to 

 the tenth dorsal vertebra, and contains the following parts : the 

 bifurcation of the trachea, the oesophagus, and pneumo-gastric 

 nerves, the thoracic duct, the vena azygos, the thoracic aorta, the 

 splanchnic nerves, lymphatic glands, absorbents, and loose cellu- 

 lar tissue. 



THE LUNGS 



Are two soft, spongy, vascular bodies, one contained on each side 

 of the cavity of the chest. Each lung resembles a cone, with that 

 side corresponding to the median line truncated ; the base concave, 

 corresponds to the diaphragm, the obtuse rounded apex rises in the 

 neck, a little above the level of the first rib ; the external convex 

 surface corresponds to the internal concave surface of the thoracic 

 parietes, and the flat or truncated surface corresponds to the me- 

 diastina. The posterior edge of the lung is thick and rounded, 

 whilst the anterior is thin and irregular. Each lung is distinguished 

 into lobes, which are separated from each other by fissures ; a little 

 above the centre of each is the root formed by the pulmonary ves- 



