86 
BUI^LETIN OF THE BUREAU OP FISHERIES 
section of the gastric walls. It is about twice the thickness of the longitudinal muscle 
sheet. 
The circular muscle is composed of smooth muscle fibers in the pyloric and lower 
three-fourths of the cardiac division of the stomach. Striated muscle cells extend 
down from the esophagus for some little distance, about one-fourth the length of the 
cardiac end. The point has been determined only in the young, where the striated 
fibers extend well below the esophageal boundary of the gastric gland region. There 
is no special peculiarity of structure of the gastric smooth muscle fibers. A rich vascular 
supply permeates this muscle coat, the blood vessels being for the most part small 
branches of the vessels lying between the two muscle coats. 
Muscularis longitudinalis . — This is the outer of the two muscle coats of the stomach. 
It is well separated from the circularis by the numerous blood vessels and bundles of 
nerves of the Auerbach plexus, together with the connective tissue supporting these 
structures. These smooth fibers are rather less compact in arrangement than the 
circularis, perhaps due to the numerous blood vessels that are found in its substance. 
This coat is of course pierced by every vessel penetrating to the deeper structures. 
The striated muscle fibers of the upper end of the stomach are not found in the longi- 
tudinal muscle. This coat is very thin over the esophageal end of the stomach. 
Plexus of Auerbach . — This nerve complex has not been sufficiently studied. It may 
be noted here, however, that the plexus is strongly developed in the king salmon stomach 
and in the other parts of the alimentary canal. Relatively large bundles of fibers are 
to be found between the two muscle coats and embedded in the longitudinal coat. 
HISTOEOGY OF THE GASTRIC SEROSA. 
The serosa of the salmon is formed by the single layer of plate-like epithelioid cells 
that is found in all the vertebrates of the higher series. Under certain conditions these 
cells become much thicker, i. e., quite cubical in shape. This form has been especially 
noted in the retrogressive changes that occur during the migration fast of the king 
salmon. 
THE INTESTINE. 
FORM AND DIVISIONS OF THE INTESTINE. 
The intestinal portion of the alimentary tract of the salmon is, like the stomach, a 
U-shaped tube. In this case the first limb of the U is relatively short. It includes that 
portion of the intestine which has the numerous diverticula, the pyloric caeca. This 
limb begins at the pyloric valve which marks the limit of the pyloric end of the stomach. 
It extends anteriorly to about the level of the point where the esophagus and stomach 
join. At this level there is a sweeping bend in the intestine from the ventral to the 
dorsal position in the celomic cavity. The intestine here takes a position along the 
dorsal lateral side of the stomach and runs a straight posterior course to the cloaca 
and vent. This straight stretch of the intestine forms the second limb of the U, and 
is considerably longer than the first limb. In the adult salmon the two divisions of 
the intestine vary in length in proportion to the length of the fish. But for an 8o-cm. 
