76 
bulletin of the bureau of fisheries 
HISTOLOGY OF THE ESOPHAGUS. 
The esophagus in the king salmon is a very short museular tube extending from 
the posterior part of the pharyngeal cavity to the stomach. The length of the 
esophagus is only 3 to 5 centimeters, even in the largest salmon. 
A cross section through the esophagus shows three coats, of which the thickest 
and most important is the muscular coat. The lining of the esophageal tube is com- 
posed of epithelium which is complexly folded and which rests upon a subepithehal 
connective tissue foundation. 
epithelial coat op the esophagus. 
The epithelial coat of the salmon esophagus consists of columnar epithelial cells. 
In the anterior portion this epithelial layer is supported by one or two irregular layers 
of deeper cells. This region represents the transitional stages between the stratified 
epithehum of the mouth and pharynx and the single layer of epithelial cells lining the 
rest of the alimentary tract. The smaller basal epithelial cells are represented for 
some little distance down the esophagus, though they are relatively few in number 
except in the region just described. 
Most of the epithelial cells have clear outer margins with a stainable protoplasm 
and the nucleus crowded to the base of the cell. This is interpreted as meaning that 
these cells are chiefly concerned with the production of mucus, that they are in fact 
mucous cells. 
The mucous coat is complexly folded. In microscopic cross section the folds are 
often cut in such a way as to simulate simple tubular glands. When the gross folds 
are unusually large then these simple tubelike appearances may be located on the sides 
of the larger folds. This is a mechanical condition which appears later, i. e., especially 
in the mucous epithelium of the intestine, and in simpler form in the caeca. In all the 
sections available the esophagus is strongly contraeted so that the epithehal coat is 
thrown into unusually rich folds. The study of cross sections leads one to the view that 
if the esophagus were fully distended most of these epithelial folds would be eliminated. 
No differentiation among the epithelial cells of the esophageal mucosa could be 
discovered. 
subepithelial connective tissue or tunica propria. 
This coat in the esophagus consists of a simple type of areolar connective tissue. 
The nuclei are small and oval, the connective tissue strands are open and especially 
loose in arrangement. Occasional blood vessels are noted in the sections. Just at 
the base of the epithelial coat the connective tissue is a trifle more dense and the fibers 
and nuelei are arranged parallel with the inner surface of the epithelial coat. No 
evidence of smooth muscle fibers or other specially differentiated cells was found in the 
tunica propria of the salmon esophagus. 
