THE ALIMENTARY TRACT. 



277 



a longitudinal slit about 3 mm. in length. The mucous mem- 

 brane to either side of the tongue is only slightly folded, and 

 a little in front of the angle of the mouth is depressed into 

 an aperture (-6'), opening into the vocal sac. This opening is sui-- 

 rounded by small radiating* folds of mucous membrane, and is oval 

 in shape. 



Towards the oesophagus the nui- -picr. lyq. 



cous membrane of both the roof c 



am 



and the floor of the mouth is thrown ^^Hk». 



into numerous longitudinal folds. /^/^\\ 



b. The minute structure of the ^~ff / ""'^.aV'i v\ 



several parts. /L ['v'"*-*/'! i*^ 



(1) The mucous mieinbrane of MW j '^'■>^^^^\^^ 



the mouth. At the junction of the M /^,^^'~''N!% '^%k- k 

 skin and the mucous membrane ^' ) c/^ '^^^ pA / 



there is a gradual transition from V whyi- Js^Èj.. 



the stratified epithelium of the . ) \ ^'mi/jiJ 



skin to a sing'le layer of eolum- KyvûSxî^'vi-iJ 



nar epithelium. On the floor The floor of the mouth. 



of the mouth this condition is k Muscles, 



11, ;i, ji L Opening to larvnx. 



reached at tlie tongue ; on the ^ Mandiwe. 



roof the transition takes place ''^ Opening to voice-sac (in males only) 



^ Sin Chin. 



more quickly. The columnar z Tongne. 



• jt t p ,■, . I /,•. , p Zl Left cornu of bifid tongue. 



epithelium Ot the mouth (that Ot t Folds opposite hinder border of the 



the tongue is excluded from this \^yo\A. 



description) is ciliated ; scattered cells, which are not ciliated, are 

 found here and there irregularly, but are not numerous. The 

 cylindrical cells are very finely granular in their upper parts, 

 clearer in the middle portion, more coarsely and darkly granular in 

 their deeper portions; each cell is possessed of a large, well-defined, 

 oval nucleus, which contains one or sometimes two nucleoli. The 

 non-ciliated cells usually present a sharply differentiated, structure- 

 less, hyaline, free border (Schultze). The epithelium towards the 

 margin of the mouth, where it is stratified, is also ciliated. 



Goblet-cells occur in every part of the epithelium, whether cili- 

 ated or non-ciliated, and their forms vary very greatly. 



[The submucous layer is a fibrous connective-tissue matrix, 

 very rich in nerves and blood-vessels. The capillaries are arranged 

 in small, somewhat polygonal meshes (Fig. iHo), and are peculiar, 

 with those of the anterior part of the oesophagus, in having- small 



