238 HISTOLOGY. 



The blood vessels form two or three networks parallel with the surface, 

 followed by a capillary plexus just beneath the epithelium. The lym- 

 phatic vessels similarly form two communicating networks, of which the 

 more superficial consists of smaller vessels and is situated beneath the 

 capillary plexus. The nerves form a deep and a superficial plexus which 

 are associated with microscopic ganglia. Non-medullated fibers end either 

 beneath the epithelium in bulbs and free endings with terminal knobs, or 

 within the epithelium in free ramifications and in taste buds. Below the 

 vocal folds, subepithelial nerve endings and buds are absent, but many 

 intraepithelial fibers occur which encircle individual taste cells. The 

 nerves and vessels of the larynx are numerous, except in the dense elastic 

 tissue of the vocal folds. The ventricular folds [false vocal cords] consist 

 of loose fatty, glandular tissue rich in vessels. 



TRACHEA. 



The trachea consists of a mucosa, submucosa, and a fibrous outer 

 layer containing the tracheal cartilages. The outer layer is continuous 

 with the tissue of the mediastinum. It forms the perichondrium sur- 

 rounding the succession of hyaline C-shaped cartilages, the free ends of 

 which are toward the oesophagus. In the interval between these ends, 

 there is a layer of transverse smooth muscle fibers, usually accompanied 

 by bundles of outer longitudinal fibers. As in the intestine, elastic fibers 

 are abundant among the muscle cells. The tracheal cartilages may be- 

 come partly calcified in old age. 



The submucosa is a layer of loose fatty connective tissue, continuous on 

 its outer side with the perichondrium. It contains the bodies of the 

 branched, mixed tracheal glands. On the dorsal or oesophageal wall of 

 the trachea, these glands are larger than elsewhere and extend into or 

 through the muscle layers. 



The mucosa is separated from the submucosa by a distinct dense 

 layer of elastic fibers, chiefly longitudinal. This layer has been com- 

 pared with the muscularis mucosae of the intestine. Between it and the 

 epithelium there is a thin layer of tissue, containing elastic fibers and 

 having leucocytes in its meshes. A basement membrane is found beneath 

 the epithelium. As in the larynx the epithelium is pseudo-stratified and 

 columnar, with cilia proceeding from distinct basal bodies. It contains 

 goblet cells. On the oesophageal surface there have been found areas 

 of non-ciliated, stratified epithelium, with connective tissue papillae 

 beneath, and squamous cells on its surface. 



