THE LUNGS. 575 



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 sympa- 

 thetic. In Man, I have myself also seen, in the pleura pulmonalis, 

 nerves, as much as 0*036 of a line in diameter, accompanying the 

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

 and occasionally large scattered ganglion-globules, which were derived 

 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 ter- 

 minations, 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 vesi- 

 cles (vesicula? 8. cellulce aereoe s. Malpig- 

 hiance, alveoli pulmonum, Rossignol), not, 

 as was formerly believed, by each finest 

 bronchial twig terminating in a single 

 vesicle, but always by their communicating 

 with a whole group of air-cells. These 

 groups of vesicles correspond to the smallest 

 lobules of racemose glands, and conse- 

 quently there is no occasion whatever to designate them under any 

 other name, as was done by Rossignol, who calls them infundibula, 

 although it must be allowed that their structure, in many respects, is 

 peculiar. For, whilst in other glands the vesicles, if not quite so isolated 

 from each other as has hitherto been supposed, still enjoy a certain 

 degree of independence, the pulmonary elements corresponding to 

 them, the air-cells, are, to a considerable extent, confluent with each 

 other, so that all the vesicles belonging to one lobule open, not into 

 ramifications of the finest bronchial twig going to it, but into a common 

 space, from which the air-vessel is afterwards developed. That this is 



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

 twigs, cc, upon which air-cells are also placed. From a new-born child; magnified 25 

 diameters. Half-diagrammatic. 



