170 
The serosa, s, is here quite indistinct. 
A transsection 
Fic. 42. 
through the posterior region 
of the cesophagus of the 
hibernating animal, under low 
magnification; e, epithelium; 
cm, circular muscles; Im, 
longitudinal muscles; mm, 
muscularis mucosa; sm, sub- 
mucosa; S, serosa. 
The Alligator and Its Allies 
It con- 
sists of a slightly vascular 
connective tissue which can- 
not be distinctly differenti- 
ated from the connective 
tissue of the longitudinal 
layer. 
In the posterior region of 
the cesophagus, as may be 
seen by comparison of figures 
41 and 42, the wall as a whole 
is about one third thicker 
than in the anterior region 
just described, though how 
much of this difference is due 
to different degrees of dis- 
tension or contraction it is 
hard to say. 
The epithelium, e, isin the 
tissue studied thrown into 
less complicated folds than 
in the anterior region, and is 
not so thick. 
The submucosa, sm, if the 
entirelayer may beso called, 
has about the same thick- 
ness and structure as in the 
more anterior region; but instead of the small 
and widely scattered bundles of longitudinal 
muscle fibers there is a distinct layer of muscle 
