The Digestive System 



i8i 



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 



m m 



Cm 



Fig. 47. A transsection of the wall of the anterior region of the small 

 intestine of the hibernating animal, under low magnification; bi, lymph 

 node; fp, 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, Im, 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 



