THE LABTNX. 



317 



Fig. 207. 



tissue. This is especially well marked on the vocal cords 

 themselves. 



Behind the vocal cords the mucous membrane 

 is much more loosely attached to the surrounding 

 structures by an extremely vascular areolar tissue. 

 The epithelium is arranged in a single layer 

 of columnar cells, among which are numerous 

 goblet-cells. In the more external parts of the 

 posterior ventricles, the mucous membrane is 

 thrown into deep folds and so forms polygonal 

 acini. In the median line of the floor of the 

 larynx and behind the false vocal cords is a 

 vertical fold of mucous membrane, which in- 

 creases in height and breadth as it proceeds 

 backwards towards the roots of the lungs. The 

 mucous membrane behind the true vocal cords 

 is extremely vascular, in the most posterior 

 portion of the larynx the blood-vessels form a capillary network 

 exactly like that of the lungs.] 



e. [The epiglottis (Fig. 206 E] is a small bilobed fold of mucous 

 membrane placed on the floor of the mouth in the median plane and 

 immediately in front of the aperture to the larynx. Between it 

 and the mucous membrane covering the arytenoid cartilages are a 

 number of large mucous glands (G r ). The epiglottis does not contain 

 cartilage; it is, however, constant in its appearance and sharply 

 marked off from the surrounding mucous membrane.] 



The Rima glottidis, seen 

 from the front. 



G Rima glottidis. 

 SB Vocal cords. 



II. THE LUNGS. 



a. General description. The lungs are two large thin-walled 

 sacs (Figs. 185 and 204 Lg and Lg 1 ]. The roots of the lungs are 

 contracted at their origin from the larynx and then expand to form 

 two ellipsoid sacs, which terminate posteriorly in bluntly-pointed 

 ends. With the exception of their roots they lie entirely free in 

 the pleuro-peritoneal cavity, and are covered by the pleuro-peri- 

 toneal membrane. In the recent state they have a bright red 

 colour due to the large supply of blood-vessels. 



b. Minute structure. 



(i) The muscular tissue of the lungs is for the most part 

 arranged in large bands, which form a coarse network on the deeper 



