1232 



THE RESPIRATORY SYSTEM 



the following descriptions pertaining to the termination of the air-tubes and to the blood and 

 Ij'mph vascular systems of the lungs and pleurae. 



Through further branching of the bronchial rami a great number of very fine bronchioles 

 [bronchioli] are reached, whose walls possess a weak muscle layer and are lined by mucosa 

 having an epithelium of flattened non-cihated cells. These, subdividing, give rise to the 

 respiratory bronchioles [bronchioli respiratorii], the walls of which are beset with alveoli 

 (fig. 992). From the respiratory bronchioles arise the alveolar ducts [ductuli alveolares], or 

 terminal bronchi, each of which leads to a group of air-spaces, called atria, each of which again 

 communicates with a second series of air-spaces, the air-sacs (alveolar sacs or infundibula), 

 whose walls are pouched out to form numerous pulmonary alveoli [alveoli pulmonum]. 



A terminal bronchus with its air-spaces and blood-vessels, lymphatics and nerves, together 

 form a pulmonary lobule [lobulus pulmonum], the unit of lung structure. 



Aeby divided the bronchial branches into tw^o sets, according to their relation to the pul- 

 monary artery. The branch arising above the place where the pulmonary artery crosses the 

 stem-bronchus he named the eparterial bronchus, and those arising below the crossing he called 

 hyparterial. An eparterial bronchus exists only on the right side ; all other branches are hy- 

 parterial. Since the eparterial supplies the superior lobe of the right lung and no eparterial 

 branch is present on the left side, Aeby concluded that the left lung had no lobe homologous 

 with the superior lobe of the right lung. He compared the middle lobe of the right with the 

 superior lobe of the left lung. The collateral branches of the stem-bronchi arise in a dorsal 

 and ventral series in the lower mammals, and the same arrangement, though less obvious, 

 obtains in man. According to the views of Aeby and Hasse, the first ventral branch of the right 

 side is distributed to the middle lobe, while the remaining three ventral and all the dorsal lateral 

 branches are given to the inferior lobe. On the left side, the first ventral branch is given to the 

 superior lobe; the other ventral branches and the dorsal branches are distributed to the inferior 

 lobe. 



Fig. 996. — Scheme of the Bronchial Tree According to Narath. A. Anterior view. B. 



Right lateral view. (Poirier and Charpy.) 

 A. Apical bronchus, collateral of the first ventral and susceptible of becoming eparterial, Ap 



in migrating to the bronchial trunk. 



Ap = Di 



Narath considers the division of bronchial liranches in accordance with their relation to 

 the pulmonary artery as of no groat iiiori)h()l()gical significance. He attributes the apparent 

 differences on the two sides to a sliifting in position of homologous l>ranches. Thus, Narath 

 considers that the eparterial bronchus of Achy has become the first dorsal lateral branch by 

 displacement above the pulmonary artery and that it is homologous with an apical branch of 

 the left side, which retains its prnnitive origin from the first ventral liranch (fig. 990). Narath's 

 conception of the migration of the l)r()iichial l)ranches is supported by the results of Hunting- 

 ton's extensive studies of the bron(;liial tree in mammals. 



The physical properties of the lungs. — Tlio average dimensions in the adult male are as 

 follows: Ileiglit of the lung is given at, 2.5-27 cm., the greatest sagittal diameter at 16-17 cm., 

 and the greatest transverse irKiasurcmciit as 10 cm. for the right and 7 (an. for the left. The 

 voluiwi of the lungs when well expanded is G.')00 c.c. (Mcrkel.) The wcighl of the hings can 

 be found only approximately on account of the presence of blood and mucus. In the adult 

 male the weight of both lungs is given as KiOO gm.; female, 102;^ gm. Tlie weight of the right 

 lung comparcid with the left is as 11 is to 10. Hied and Hutchinson found the weight of the 

 lungs compared with that of the body as 1 :'M (male), 1 A'A (female); in the f(rtus at term, 

 1:70. After resi)iration has l)een established, the lung, if jilacod in water, will float. Its 

 specific (jravih/ is between O.^ilf) and ().71(). (Haiiber.) The f(i>tal lung contains no air and is 

 heavier than water. Its specific gravity is 1.04.5 to 1.0r)(). (Kraiise.) Lung tissue, free of 

 air, with vessels moderately filled, has likewise a sijccific gravity of 1 .04r) to l.or)(). (Vierordt). 



Th(! colour of the lung result sl'nmi t he presence of blood, jjigmeiit, and the air in the alveoli. 

 It varies therefore as these constituents arc .all or in part present and with differences in tlieir 



