The Digestive System 



169 



mb 



It is composed of a fairly dense mass of connective 

 tissue, mainl}'- elastic fibers, through which are 

 scattered small blood-vessels, bv, and small dark 

 areas, nib, that are appar- 

 ently longitudinal bundles 

 of involuntary muscle fib- 

 ers. These few and scat- 

 tered fibers probably 

 represent the muscularis 

 mucosa that is so well 

 developed in the poster- 

 ior region of the oesoph- 

 agus. 



Outside of the mucosa 

 is a thick circular layer of 

 involuntary muscle fibers, 

 cm, the fibers being col- 

 lected into irregular bun- 

 dles, between which are 

 narrow spaces filled with 

 connective tissue that con- 

 tains a few small blood- 

 vessels. 



Surrounding the circu- 

 lar layer is a thinner and less clearly defined layer 

 of longitudinal m.uscle fibers, hn. The muscle 

 bundles are more definite than in the circular layer 

 and are separated from each other by a consider- 

 able amount of connective tissue with a few small 

 blood-vessels. 



'S-- ,lfn 



Fig. 41. A transscction 

 through the anterior region of the 

 oesophagus of the hibernating 

 animal under low magnification 

 hv, blood-vessels; mb, muscle 

 bundles; other letters as in Fig- 

 ure 42. 



