THE RESPIRATORY TRACT. 267 



If the lung be pencilled before it is treated with the silver 

 solution the deeper structures can be examined. The sections 

 should be mounted in glycerine with the external surface 

 upward. The appearances here are similar to those already 

 described. The capillary lymphatic-vessels communicate with 

 the superficial pulmonary branches forming the subpleural 

 lymphatics. 



The endothelial cells of the pulmonary pleura vary in 

 shape according to the degree of distention of the lung. In 

 the lung which has been inflated before hardening, the cells 

 appear as flat plates, but in the atelectatic lung of a fetus, or 

 the collapsed lung of an animal that has breathed, they are 

 cubical or even columnar in shape. This difference is most 

 marked in the guinea-pig, owing to the presence of a layer of 

 muscular-fibres beneath the pleura of that animal. The tops 

 of the cells which have this pyramidal shape are not flat as in 

 true columnar epithelium, but rounded. This change of shape 

 simply indicates that the cells accommodate themselves to 

 changes of space. These changes, in a lesser degree, must be 

 occurring constantly during life, with the movements of respi- 

 ration. On the costal pleura, the stomata are only found in 

 the intercostal spaces. 



Attached to the lower border of the lung are minute ap- 

 pendages, the "pleural appendages" forming a sort of fringe 

 connected with the pleura. Some are visible to the naked 

 eye, some microscopic. The larger are made up of connective 

 tissue and blood-vessels, and, exceptionally, nervous fibres in 

 the larger ones. They are covered by round cells, sometimes 

 resembling epithelium. The smallest ones are structureless, 

 and in general have no epithelial covering. 1 



BIBLIOGRAPHY. 



COYNE, P. Recherches sur 1' anatomic normale de la nraqueuse du Larynx. Ar- 

 chives de Physiologic, p. 92. Paris, 1874. 



STIRLING. Nervous Apparatus of the Lung. Brit. Med. Journal. Vol. II., p. 401. 

 1876. 



CADIAT. Des rapports entre le develop, du poumon et la structure. Jour, de 

 1'anat. et de la Phys., No. 6, p. 591. 1877. And, Structure et de>el. du 

 poumon. Gaz. Med. de Paris, No. 17, p. 214. 1877. 



1 Luschka : Anatomic des Menschen, Bd. I., S. 293. 



