THE LUNG 



313 



These pleural pores have been the subject of considerable discussion. 

 They have been regarded by some as giving direct vent to lymphatics; 

 but Walters (Anat. 

 Hefte, Bd. 46, 1913) has 

 quite conclusively shown 

 that they are artifacts, an 

 interpretation maintained 

 also by Miller. 



The connective tissue 

 contains an abundant 

 network of elastic fibers. 

 It is loosely attached to 

 the chest wall but is more 

 firmly united to the pul- 

 monary tissue. Normally 

 the pleura contains no 

 lymph nodes ^(Miller) . 



The pleura contains 

 many small blood-vessels 

 and an abundant plexus 

 of blood and lymphatic 

 capillaries. Its innerva- 

 tion includes both sym- 

 pathetic and cerebral (vagus) fibers. Both are apparently non-medul- 

 lated. The sympathetic nerve fibers are supplied to the walls of the 

 blood vessels ; they are vasomotor in function. The vagus fibers are sen- 

 sory in nature, and terminate in lamellar corpuscles, and as fine free 

 sensory fibers. 



FIG. 296. TRANSECTION OF THE PLEURA OF AN 

 INFANT. 



a-a, layer of mesothelium; 6, submesothelial con- 

 nective tissue; c, pulmonary alveoli; d, a small blood- 

 vessel. Hematein and eosin. Photo. X 470. 



FIG. 297. FROM A SECTION OF THE PLEURA OF MAN. 



The elastic tissue appears black, a-a, mesothelial surface; b-b, submesothelial 

 connective tissue. Weigert's elastic tissue stain, hematein and picrofuchsin. X HO, 



