THE LUNGS. 



173 



fibrous tunic of the bronchia, entirely deprived of the smooth 

 muscles, and consisting of a homogeneous matrix of connective 

 tissue, together with elastic fibres and numerous vessels. The 

 elastic fibres, 0*0005 — O'OOS'" in size, present the form chiefly 

 of separate trabecule and filaments, running especially at the 

 angles of the air-cells, which have been flattened in the dis- 

 tended condition, as well as around their openings ; they anas- 

 tomose with each other on every side and thus constitute a 

 firm frame, on which the softer, vascular parts of the air- 

 alveolae, composed of connective tissue, are stretched. The 

 structure of these elastic trabecule, which, at the points where 

 the air-cells abut upon each other, mutually coalesce, so that 

 the boundaries of the separate cells cannot for the most part 



be recognised, is almost 



J° ' c ., Fig. 238. 



everywhere one of the 

 most close elastic net- 

 works possible, the in- 

 terstices of which appear 

 only as extremely nar- 

 row fissures, although oc- 

 casionally the fibres are 

 more loosely united, so 

 that they are plainly 

 recognisable as elastic 

 elements of the usual 

 kind. From the trabe- 

 cules also, but everywhere 

 sparingly, elastic fibres, 

 in part very fine, pro- 

 ceed into the remainder 

 of the walls of the air- 

 cells, in which, by their 

 union, they constitute a wide network. The connective tissue 

 of the air-cells, which appears to be altogether homogeneous, is 

 quite a subordinate element in their composition, compared 

 with the elastic elements and vessels, presenting itself, as it may 

 be said, only in the walls of the alveoles, between the elastic 



Fig. 238. Human air-cell, with the surrounding tissues, x 350 diam.: a, epithe- 

 lium ; b, elastic trabecules ; c, more delicate wall between the latter, with finer elastic 

 fibres. 



