DISSECTING MANUAL. 



descend in the mesial plane. The right line continues in this 

 plane to the ensiform cartilage, while the left line deviates 

 slightly outward, opposite the fourth costal cartilage, and then 

 descends. The costal and diaphragmatic pleurae are contin- 

 uous (diaphragmatic line) along a curved line running a short 

 distance above (except near the spine) the lower border of the 

 thoracic wall, its lowest point being in the midlateral line. 

 The diaphragmatic line, at its ends, joins the anterior and pos- 

 terior lines ; below it there is no pleura between the Diaphragm 

 and chest wall. [979] 



Mediastinal Space. This lies between the pleural sacs and 

 is arbitrarily divided by the pericardium into four portions, 

 viz. : The superior mediastinum lies above the pericardium and 

 is bounded below by a plane drawn from the lower border of 

 the manubrium to that of the fourth dorsal vertebra. The 

 middle mediastinum is the part containing the pericardium. 

 The anterior mediastinum is the part in front of the pericar- 

 dium, and the posterior mediastinum the part behind. [982] 



Lungs. The lungs are soft, spongy, elastic, and of the shape 

 of their cavities ; the right one is the shorter, wider, and slightly 

 the larger. Each has an apex, base, two surfaces, and two bor- 

 ders. The apex is rounded and rises half an inch to an inch 

 and a half above the clavicle; it is grooved by the great ves- 

 sels. The base is semilunar, concave, and has a thin margin, at 

 the sides and behind, which descends to the level of the eighth 

 rib in the midlateral line; below the margin is found a nar- 

 row pleural recess (phrenico-costal sinus) . The outer surface is 

 convex and grooved by the ribs. The inner surface presents a 

 concavity for the pericardium, and above and behind this a 

 wedge-shaped depression (hilus) where the structures of the 

 root enter. The posterior border is long, thick, and rounded; 

 it descends as far as the tenth dorsal spine. The anterior bor- 

 der is short, very sharp, and prolonged into the narrow pleural 

 recess (costo-mediastinal sinus) behind the sternum. On the 

 right side it fills the recess; on the left side, over the apex of 



[138] 



