The Digestive System 181 
At the outer border of the tunica propria, and 
with no tissue corresponding to a submucosa 
between it and the circular muscular layer, is a 
thin and indistinct layer that has the appearance 
Fic. 47. A transsection of the wall of the anterior region of the small 
intestine of the hibernating animal, under low magnification; Jn, lymph 
node; ép, tunica propria; other letters as in Figure 42. 
of a longitudinal layer of muscle fibers; this should 
correspond to the muscularis mucosa (Figs. 47, 48, 
49, and 51, mm). 
The circular, cm, and longitudinal, lm, muscle 
layers are compact, and are distinct from the 
other layers of the wall; the former is approxi- 
mately twice the thickness of the latter. The 
relative thickness of all the layers in the three 
