54 THE LUNGS, BY FRANZ EILHARD SCHULZE. 



The plates are then irregularly distributed, become gradually 

 smaller, and separated by wider intervals, until they are com- 

 pletely isolated, and are chiefly found at the angles of division 

 in the form of thin discs or clasps, finally disappearing in 

 bronchia of less diameter than T5 1 millimeter. In very 

 small Mammals, as in the Mouse and a few Bats, e.g., Ves- 

 perugo pipistrellus, in which the largest bronchia scarcely 

 attain this size, the cartilage may be altogether absent in the 

 lungs. 



A peculiar structure is presented by the bronchial cartilages 

 in consequence of the following special arrangement of the 

 numerous cells contained in the hyaline matrix. Whilst the 

 flat cake-like cells of the cortical layer of the cartilage-plate are 

 everywhere placed with their broad surfaces parallel to that of 

 the lamina, the more rounded internal cells, which often form 

 elongated groups, being held together by the so-called secondary 

 cartilage capsules, are arranged in rows perpendicular to the 

 surface ; so that if we particularly examine the solid matrix 

 of the cartilage, the two cortical layers arranged parallel to 

 the terminal surfaces appear to be connected by transverse 

 braces. 



The fibrous tissue constituting a perichondrium to the carti- 

 lage where this is present, consists of closely arranged longitu- 

 dinal fasciculi of connective tissue traversed by thinner circular 

 layers, the two being even occasionally disposed in alternate 

 laminse, especially in the outer part of the membrane. It 

 contains also longitudinal plexuses of fine elastic fibres, which 

 become thicker and more abundant, where they extend from 

 the thin border of one cartilage to the next, connecting the two 

 in the direction of the long axis of the bronchia. 



Whilst small masses of fat are found to be more or less abun- 

 dantly distributed in the outer portion of this fibrous layer, the 

 inner presents mucous glands, the number and size of which 

 diminish in a proportion corresponding with that of the tube. 

 These occupy in the larger bronchia, not only the intervals of 

 the cartilages, where the parietes of the tube are composed of 

 fibrous membrane by which their growth is unimpeded, and 

 where they often attain a considerable size, extending far into 

 the outer layer of the membrane, but also on the inner surface 



