244 



THE RESPIRATORY SYSTEM 



nective tissue contains an abundant network of elastic fibres. It 

 is loosely attached to the chest wall but is more firmly united to 



the pulmonary tissue. 

 The pleura contains 



many small blood vessels 



and an abundant plexus 

 of blood and lymphat- 

 ic capillaries. Its non- 

 medullated nerve fibres 

 are mostly supplied to 

 the walls of the blood 

 vessels ; some, however, 

 terminate in Pacinian 

 corpuscles and in fine 

 sensory terminal 

 branches. 



THE LOBULE OF 

 THE LUNG. If care- 

 fully examined, the sur- 

 face of the pulmonary 

 pleura presents minute 

 polygonal areas, the 

 bases of the anatomical 

 lobules, whose borders mark the attachment of fine bands of in- 

 terlobular connective tissue. In microscopical preparations still 



FIG. 206. TBANSECTION OF THE PLEUBA OF AN 



INFANT. 



o-a, layer of endothelium ; , subendothelial con- 

 nective tissue ; c, pulmonary alveoli ; rf, a small blood 

 vessel. Hematein and eosin. Photo, x 470. 



FIG. 207. FROM A SECTION OF THE PLEURA OF MAN. 



The elastic tissue appears black, a-a, endothelial surface ; b-b, subendothelial connec- 

 tive tissue. Weigert's elastic tissue stain, hematein and picro-fuchsin. x 110. 



finer bands may be found, which traverse the pulmonary tissue 

 in the direction of the root of the lung, and which partially out- 

 line minute conical areas, the true pulmonary lobules, whose bases 



