CHAPTER XVI. 



THE INTESTINAL CANAL.* 



BY E. KLEIN AND E. VERSON. 



A. ORAL CAVITY, BY E. KLEIN.. 



THE mucous membrane of the oral cavity in man begins at 

 the lips as a direct continuation of the outer integument. 



Three anatomically different partsf can be distinguished in 

 it : a cutaneous, a transitional, and a muco-membranous portion. 



The transitional portion is marked off from the cutaneous 

 portion by the outer border of the red lips, and from the muco- 

 membranous portion by the most prominent part of the con- 

 vexity of the lips, so that when the mouth is closed the red 

 visible portion of the lips represents the transitional portion. 



The cutaneous portion is covered by a thin epidermis con- 

 sisting of one or two layers of flattened epithelium intimately 

 fused with one another ; subjacent to this is a thinner mucous 

 layer, in which are small rounded cells containing relatively 

 large nuclei. 



The cutis internal to this is composed of fasciculi of fibres, 

 which decussate with one another, the principal ones being 

 directed towards the free border of the lips. The fibres which 

 form these fasciculi consist, for the most part, of fine connective 



* The account given in this section rests on investigations which the 

 authors have undertaken in my laboratory for this work. S. STRICKER. 



t E. Klein, Zur Kenntniss des Baues der [Mundlippen des neugebornen 

 Kindes, " On the Structure of the Oral Lips of the newly born Child;" 

 Sitzungsberichte der k. k. Akadem. der Wissenschaften in Wien, December 

 Heft, 1868. 



