1850 



HUMAN ANATOMY. 



vessels. Each lobule is entered by an intralobular bronchus (.5-1 mm. in diam- 

 eter), accompanied by its artery, not quite at the apex of the pyramid, but slightly 

 to one side of it. The bronchus divides into two, at an angle of from 9O-ioo, a 

 link- above- tin- middle of the lobule, having previously given off two or three col- 

 lateral branches to its upper part. In the third 

 quarter of the lobule the two subdivisions ( 2-3 

 mm. in length ) again split, with about the same 

 degree of divergence as the parent stems, but in 

 a plane at right angles to that of the previous 

 splitting. Tins is repeated in three or four suc- 

 cessive bifurcations, a varying number of col- 

 lateral branches being given off. Thus the num- 

 ber of branches in the third quarter is much in- 

 creased ; but it is in the last quarter and towards 

 the periphery of the lobule throughout that the 

 tubes break up into the great number of truly 

 ultimate bronchi. The various collaterals, spread- 

 ing and even reascending, undergo subdivision 

 also. Laguesse and d' Hardiviller ' estimate the 

 number of terminal bronchi (ductuli alveolares) 

 within a single lobule at from fifty to one hun- 

 dred or even more. The slightly dilated distal ex- 

 tremity of the terminal bronchus communicates 

 with from three to six spherical cavities, the atria 

 of Miller' 1 (so named by him from the resemblance 

 to the arrangement of an ancient Roman house). 

 The atria, in turn, communicate with a group of 

 larger and irregular cavities or air-sacs (sacculi 

 alu-olarcs '. into which directly open the ultimate air-spaces, the alveoli or air-cells 

 ( alveoli pulmonis ). The latter open not only into the air-sacs, but also into the atria, the 

 dilated distal part of the terminal bronchus being likewise beset with scattered alveoli. 

 Miller holds that the terminal bronchus, the air-chambers connected with it, 



together with the vessels and 



Diagram showing relations of terminal sub- 

 divisions of air-tubes, fi, bronchiole ending in 

 terminal bronchi ( TB) ; latter divide into atria 

 (A), each of which communicates with several 

 air-sacs (s) into which open the alveoli (a) ; 

 PA, branch of pulmonary artery follows bron- 

 chiole ; Py, pulmonary vein at periphery of 

 lung-unit. (After Miller.) 



FIG. 1572. 



'|..u:iii..n ,.i lung. showinj? lunR-units. a, 

 .,.I,,, K m i,.,,,,,,,.,l l.i..,,. I,,,A, A, , . . .aria; rf, air-sac 



bronchus 

 li! 



nerves, is the true lung-unit, 

 and calls it the lobule. We 

 cordially agree that this is 

 the true lung-unit, and pro- 

 pose that name for it, retain- 

 ing the term ' ' lobule' ' 

 the above-described more o; 

 less isolated portion of the 

 lung which is surrounded b 

 connective tissue and vesse! 

 and receives a single intra 

 lobular bronchus and artery, 

 In some animals the lobules 

 are perfectly distinct ; they 

 may be isolated in the infant, 

 and can be in the main easily 

 made out in the adult. Th 

 lung-unit, on the other han 

 is not surrounded by areol 

 tissue, and its limits can 

 determined only by recon 



\ 



f'o.n mi, ros, opioal sections ; hence, apart from its minuteness, it is practi 

 soLtlnrJ T'm .iil an * traCtl n tO deserve the name almost universally applied t( 



'BibKographfa Aiutomique, 1898. 



'Journal ol .Mur,,i,l, y , ,893. Archiv f. Anat. u. Phys., Anat. Abth., 1900. 



