CHAPTER IX. 

 RESPIRATORY SYSTEM. 



Trachea. T.S. Dog. (p. 8, s. 22 P* & 24, c. P., m. B.) (L) An 

 incomplete ring of cartilage, the posterior ends of which 

 overlap and are united by the trachealis muscle. The peri- 

 chondrium passes internally into the looser submucous tissue, 

 in which note mucous glands. The inner surface has a 

 well-defined edge, which recognise (H) to consist of many 

 layers of epithelium. The surface cells are columnar-ciliated. 

 Examine the shapes of the cells in the different layers and 

 the surface upon which they rest. 



Large bronchus in the lung. Sheep or cat. (p. 8, 

 s. 22 & 24, c. P., m. B.) (L) Find bronchi cut across, in 

 bronchial tracts, surrounded by but sharply mapped off from 

 the vesicular lung substance. The thick-walled bronchus is 

 associated with the pulmonary artery and vein, which usually 

 lie on opposite sides of it to form the tract, an arrangement 

 which becomes less regular peripheralwards. (If) The epithelial 

 layer of the mucosa lining the inner surface of the bronchus 

 is wavy (sectional view of longitudinal corrugations), and per- 

 forated by the ducts of the mucous glands. Externally beneath 

 the sharply-defined surface of attachment of the epithelium 

 note the layer of transversely cut elastic fibres, and next a 

 continuous band of non-striped (bronchial) muscle. Between 

 the latter and the plates of cartilage are disposed the mucous 

 glands, interspersed with variable quantities of adenoid tissue 

 (lymph cords, Klein), and areolar tissue. The perichondrial 

 extensions form a continuous fibrous covering around the 



