THE LUNGS. 319 



borders of the alveoli is a short columnar ciliated epithelium (Fig. 

 208) ; such epithelium is also found in the root of the lung- ; it 

 contains goblet-cells. 



The alveoli, for the most part, are lined with a single layer 

 of tesselated epithelium; the cells are polygonal in outline, 

 with finely granular contents and a distinct nucleus : the average 

 diameter of the cells is from 0*0074 to o*oio8 mm., that of the 

 nucleus 0'0054 mm., that of the nucleolus o'oooç mm. ; four to 

 eight of such cells occupy the space enclosed by one mesh of the 

 capillary network (Eberth). 



The epithelium rests on a structureless basement membrane, which 

 is continuous over the whole inner surface of the lung, whereas the 

 epithelium does not pass over the capillaries, and is therefore only 

 found in isolated patches in the areas enclosed by the capillaries 

 (Eberth). 



In various isolated spots, small groups of short columnar or 

 goblet-cells are found in the tesselated epithelium (Eberth, Hoff- 

 mann). 



(5) [The lymphatics of the lungs have been described by T. Hoff- 

 mann; they form a network of vessels surrounding the larger 

 blood-vessels : from this branches are given off, which form a 

 network of fine canals through the whole of the lung ; part of this 

 secondary network accompanies the blood- capillaries, but other 

 portions run a separate course. They communicate with the 

 pleuro-peritoneal cavity. 



(6) The pigment-cells are very numerous, branched, and large ; 

 they accompany the lymphatics, and not the blood-vessels (T. Hoff- 

 mann). 



(7) The nerves of the lungs (p. 172) course along the larger blood- 

 vessels, under the serous coat; the fibres are chiefly medullated 

 fibres (Egorow, Kandarazki). Non-medullated branches, which form 

 a plexus in each alveolus, are given off. The branches have small 

 triangular enlargements (ganglia), where they unite. The nerves 

 are accompanied by nerve-cells, which occur either singly or in 

 groups. 



Egorow describes the nerves as being distributed in three net- 

 works : one for the mucous membrane and muscular trabeculae; a 

 second for the superficial muscular layer ; and a third for the serous 

 membrane.] 



