THE LUNGS 53 X 



third of its original size, and loses its proper form; this is due to its highly elastic 

 character and the fact that the tension of the lung tissue caused by the air pressure 

 m its cavities has been relieved by the external air pressure.i The color varies 

 according to the amount of blood contained in the lung. During life the lung has a 

 pink color, but in subjects which have been i bled for dissection it is light gray or 

 f amtly tinged with red. In unbled subj ects it is dark red ; the depth of color varies, 

 and is often locally accentuated by gravitation of blood to the most dependent parts 

 (hypostasis). The foetal lung, since it contains no air and has a relatively small 

 blood-supply, differs from that of an animal which has breathed in the following 

 respects: (1) It is much smaller; (2) it is firmer and does not crepitate; (3) it sinks 

 in water; (4) it is pale gray in ,color. In form the lungs are like casts of the cavities 

 in which they are situated. When well hardened in situ, their surfaces present 



bo r 



der 



Fig. 472. — Right Lung of Hoese; Costal Surface. 

 Specimen hardened in situ. 



impressions and elevations corresponding exactly to the structures with which they 

 are in contact. Each lung presents two surfaces, two borders, a base, and an apex. 



The costal surface (Fades costalis) is convex, and lies against the lateral 

 thoracic wall, to which it is accurately adapted. 



The mediastinal surface (Facies mediastinalis) is much less extensive than the 

 costal surface. It is molded on the mediastinum and its contents. It presents a 

 large cavity adapted to the pericardium and heart; this is termed the cardiac 

 impression (Impressio cardiaca), and is larger and deeper on the left lung than on 

 the right. Above and behind this is the hilus of the limg (Hilus pulmonis), at which 

 the bronchus, vessels, and nerves enter the lung; the bronchial lymph glands are 

 also found here. Behind this the two lungs are adherent to each other over a 

 triangular area. Above this there is a groove for the oesophagus, which is deepest 

 on the left lung. A groove for the aorta (Sulcus aortae) curves upward and back- 

 ward over the hilus, and passes backward near the dorsal border of the lung; the 



^No idea of the natural form and size of the lung can be obtained from a specimen in this 

 state, nor can an accurate conception be gained by examination of the soft inflated organ. The 

 lungs should be hardened in situ for this purpose, and if the process has been successful they con- 

 form in every detail to the structures with which they were in contact. 



