310 THE ORGANS 



Lymphatics form plexuses in the submucosa and mucosa, the 

 most sui)erricial lying just beneath the subepithehal capillary plexus. 



The nerves of the larynx and trachea are derived from both cere- 

 bro-spinal and sympathetic systems. The cerebro-spinal nerves are 

 afferent, the dendrites of spinal ganghon cells. They form a sub- 

 epithelial plexus from which are given off fibrils which pass into the 

 epitheUum and terminate freely among the epithehal cells. Other 

 afferent fibres of cerebro-spinal nerves pass to the muscular coat of 

 the trachea. Sympathetic nerve fibres form plexuses which are inter- 

 spersed with minute groups of ganghon cells. Axones from these 

 ganghon cells have been traced to the smooth muscle cells of the 

 trachea. Sympathetic axones also pass to the glands of the trachea 

 and larynx. On the under surface of the epiglottis small taste buds 

 are found. 



TECHNIC 



(i) For the study of the details of structure of the walls of the nares and 

 larynx, fix small pieces of perfectly fresh material from different regions in 

 formalin-Miiller's fluid (technic 6, p. 7), harden in alcohol, stain sections with 

 haematoxylin-eosin (technic i, p. 20), and mount in balsam. 



(2) The general relations of the parts can be studied by removing the larynx, 

 upper part of the trachea, and corresponding portion of the oesophagus of an 

 animal or of a new-born child, fixing and hardening as above, and cutting longi- 

 tudinal sections through the entire specimen. 



(3) Trachea.- — Remove a portion of the trachea and treat as in technic (i). 

 Both longitudinal and transverse sections should be made; the longitudinal in- 

 cluding at least two of the cartilaginous rings; the transverse being through one 

 of the rings. 



The Bronchi 



The primary bronchi and their largest branches have essentially 

 the same structure as the trachea except that the cartilaginous rings 

 are not as complete. Bronchi branch at acute angles and also give 

 off small side branches. 



As they decrease in calibre, the following changes take place in 

 their walls (Figs. 208 to 211). 



(i) The epitheUum gradually becomes thinner. In a bronchus 

 of medium size (Fig. 208) it has become reduced to three layers of 

 cells, which Kolliker describes as an outer ''basal" layer, a middle 

 "replacing" layer, and a surface layer of cihated and goblet cells. 

 In the smaller bronchi (Figs. 210, 211) the epithelium is reduced to a 



