ALIMENTARY TRACT OF THE KING SALMON 
91 
MusctUaris longitudinalis . — The outer intestinal muscle coat consists of longi- 
tudinal fibers. It is a rather thin coat composed of smooth fibers and carrying numerous 
small blood vessels within its mass or between it and the inner coat. The presence of 
the small blood vessels tends to break up to some extent the compactness of arrange- 
ment of the muscle fibers. 
Plexus of Auerbach . — This nervous structure is quite prominent in all sections 
through the alimentary canal. It, however, has not yet been studied in detail for the 
salmon. The ganglia and the bundles of fibers of the plexus lie between the two muscle 
coats but rather largely imbedded in the inner wall of the outer coat. 
histology of the serosa. 
The serous coat of the salmon intestine is composed of a single layer of epithelia 
cells and the subserous supporting connective tissue. These cells are not so flat and 
attenuated as is usually the case for this coat in the intestines of mammals, but are 
more nearly cubical in shape, often quite cylindrical. Especially when the intestine 
is contracted are the cells of the serosa deeper than wide. 
The subserous connective tissue is rather prominent in the salmon intestine. It 
con^sts of white fibrous connective tissue about twice as thick in total mass as the 
epithelial coat proper. 
HISTOLOGY OF THE PYLORIC CAECA. 
Oppel says, in volume ii of Mikroskopische Anatomie, that “the pyloric caeca, 
when they exist, possess the structure of that portion of the alimentary tract on which 
they are attached.” Gulland says of the caeca of the Scottish salmon that “in structure 
they exactly resemble the upper part of the intestine, so much so in fact that but for the 
difference in size it would be impossible to say whether a section came from one or the 
other.” In the king salmon, too, the pyloric caeca are diverticula of the pyloric limb 
of the intestine, and one would naturally expect them to have a structure built on the 
same plan as the intestinal region from which they arise. This in general is true, though 
the pyloric portion of the intestine is so broken up by the origin of the numerous caeca 
that the intestinal structural constants are not altogether simple in this region. 
The coats described above for the intestine are all present in the walls of the pyloric 
caeca. The only difference is one of relative complexity, or one might rather say sim- 
plicity, of arrangement. The parts enumerated from the lumen toward the outer wall 
are: 
I. Mucosa. 
1. Epithelium. 
2. Tunica propria. 
3. Stratum compactum. 
4. Stratum granulosum. 
II. Muscularis. 
1. Circularis. 
2. Longitudinalis. 
III. Serosa. 
1 . Serosa proper. 
a. Subserosa. 
