168 



SPECIAL HISTOLOGY. 



more scantily supplied by the intercostal and mammary arte- 

 ries. Luschka found nerves with finer and coarser fibres and 

 traced them, in the outer portions of the membrane, to the 

 phrenic and to the thoracic divisions of the sympathetic. In 

 Man, I have myself also seen, in the pleura pulmonalis, nerves, 

 as much as 0-036'" in diameter, accompanying the branches of 

 the bronchial arteries, with middle-sized and thick fibres and 

 occasionally large scattered ganglion-globules, which were de- 

 rived from the plexus pulmonalis, and were probably afforded 

 chiefly by the vagus. 



§ 176. 

 Air-vessels and cells. — When the right and left bronchi 

 have reached the root of the lungs, they begin to branch, like 

 the excretory ducts of one of the larger glands, such as the 

 liver, dividing, for the most part, dichotomously and at acute 

 angles, into smaller and smaller branches; but giving off, at the 

 same time, from the sides of the larger and middle-sized 

 branches, numerous minute air-vessels, at a right angle, which, 

 like the terminations of the main ramifications, subdivide in an 

 arborescent manner. Thus is ultimately constituted an 



extremely rich tree of air-vessels, 

 whose finest terminations, never 

 anastomosing, extend through the 

 entire lung and are to be found in 

 every part, on the surface as well 

 as in the interior. With them, 

 also, are connected the ultimate 

 elements of the air- passages — the 

 air-cells or pulmonary vesicles 

 (vesiculce s. cellula aerece s. MaU 

 pighiance, alveoli pulmonum, Ros- 

 signol), not, as was formerly be- 

 lieved, by each finest bronchial 

 twig terminating in a single vesi- 

 cle, but always by their communi- 

 cating with a whole group of air-cells. These groups of vesicles 



Fig. 236. Two small pulmonary lobules, a a, with the air-cells, b b, and the finest 

 bronchial twigs, c c, upon which air-cells are also placed. From a new-born child, 

 x 25 diam. Half-diagrammatic. 



Fig. 236. 



