THE RESPIRATORY TRACT. 257 



in sections of the hardened larynx. They are lined by cubical 

 glandular epithelium. The capillary blood-vessels of the laryn- 

 geal mucous membrane are small with wide meshes, giving the 

 membrane a paler appearance than that of the pharynx. 



The lymphatics are numerous in the mucous and sub- 

 mucous layers. They may be injected with Berlin blue, by 

 puncturing the submucous tissue. 



In the nervous filaments are ganglion cells. The mode of 

 termination is not definitely known. But in the mucous 

 membrane of the epiglottis end bulbs have been found. The 

 methods of examination will be found elsewhere. 



The trachea and primary bronchi. The rings of the trachea 

 and bronchi are composed of hyaline cartilage. Longitudinal 

 sections of these rings show that the cells lying near the peri- 

 phery, underneath the perichondrium, are flattened, and ar- 

 ranged with their long axes parallel to the surface. Internally 

 they are oblong and perpendicular to the former. 



The ends of the incomplete rings are connected, posteriorly, 

 by a layer of smooth muscular fibres, which are attached to 

 the fibrous tissue of the perichondrium. The attachment is 

 to the inner aspect of the ends of the cartilages, so as to throw 

 the muscular layer forward of the most posterior projection of 

 the rings. 



These muscular fibres also exist in the spaces between the 

 rings, where they are attached, on either side, to the fibrous 

 tissue of the tube. Outside of the transverse fibres are a few 

 filaments which have a longitudinal direction. They are at- 

 tached to the fibrous membrane. 



The fibrous membrane which encloses the cartilages and 

 completes the framework of the tube is composed of connective 

 tissue containing a considerable portion of elastic tissue, par- 

 ticularly in its external portion. The outer laj r er of the fibrous 

 membrane encloses both the cartilages and the muscle fibres. 

 The inner layer is thin and lies between the rings and the 

 glandular layer. 



The mucous membrane is covered by several layers of epi- 

 thelial cells, the deeper being more or less spherical or ovoid, 

 whilst the superficial ones are columnar and ciliated. The 

 columnar cells, losing their cilia, are continued into the ducts 

 of the mucous glands. These glands are very numerous, and 

 often of considerable size. They are racemose, the acini being 



