2O Practicum III. The Lungs. 



viscera present the same appearance. Later it will be shown that the 

 serosa lining the walls, the PARIETAL PLEURA, and that which covers the 

 contained organs, the VISCERAL PLEURA, are continuous with each other. 



19. The Lungs. There are visible three LOBES of the RIGHT LUNG 

 (PI. VII), cephalic, caudal 9O&intermediate; the last is as if wedged between 

 the other two, and does not, like them, reach the dorsal wall. The 

 HEART is the darker, rounded organ, near the sternum and partly covered 

 by the lungs. 



20. Demonstrate the Lungs by inserting into the trachea a blow- 

 pipe or a glass tube and inflating moderately ; when the inflation ceases 

 they collapse. 



a. The lungs are in an unnatural condition because, for the sake of complete preser- 

 vation, alcohol was injected into them ; in a fresh state they would collapse much more 

 completely as soon as the thorax is opened ; see the lecture on Respiration. 



2i. Lift the cephalic lobe of the lung, so as to expose the constrict- 

 ed neck by which it is attached ; note that the pleura is continuous over 

 its margin and upon the mesal surface, and that at the root it is reflected 

 in all directions ; it is thus continuous with the pleura which lines the 

 thoracic cavity. 



22. With the scissors amputate the cephalic and intermediate lobes 

 so as to leave a little stalk of each as in PI. VII. 



a. Compress either of them ; a frothy mixture of air and liquid will 

 escape from the cut end of a tube, BRONCHIOLUS, a subdivision of the 

 BRONCHUS or primary division of the trachea. 



b. Inflate either lobe, holding it between the eye and the light ; at 

 the margin note the partitions between the ALVEOLI or air-sacks (some- 

 times called "air-cells"), the termination of the air-tubes, the smallest 

 subdivisions of the bronchioli. 



c. Slit up a bronchiolus and note that its rather stiff walls have the 

 cartilaginous rings complete, unlike the trachea. The other tubes in the 

 lungs are branches of the PULMONARY ARTERY and VEINS. 



23. Lift the caudal lobe and note that the pleura is reflected from 

 not only its root, but part of its dorsal margin ; this margin is therefore 

 bound to the thoracic wall by a thin sheet of serosa which appears to be 

 single ; in reality it is double, since one layer comes from one side of the 

 lobe and one from the other ; PL VII, Mpn. Remove this lobe like the 

 others. 



24. The Right Thoracic Cavity. The interior of the right half of 

 the thorax is now substantially as represented in PI. VII ; Study this 

 plate and its description. 



25. 'I he Azygous Lobe. Besides the three lobes already examined 

 the right lung has a fourth or AZYGOUS LOBE, lodged in a sort of pocket 

 in the angle between the heart and the caudal lobe ; that it belongs to 

 the right lung may be determined by gently withdrawing it from the 

 pocket. 



26. The Great Veins. At the margin of the pocket is a large vein, 

 probably containing blood ; this is the POSTCAVA (vena cava inferior or 

 "ascending cava") bringing blood from the abdominal viscera and legs to 

 the right auricle. The similar vein extending cephalad from the auricle 

 is the PRECAVA, vena cava anterior or "descending cava") bringing blood 

 from the head and arms. Joining the gjecava just cephalad of the 

 cephalic lung root is the RIGHT AZYGOUS VEIN. ' 



