Gary Radice Radice at radice at
Tue Feb 21 17:57:39 EST 1995

>>Are lips part of the digestive system or the tegumentary system? Also 
>>does anyone have any ideas about the evolutionary trends of lips!!
>>Thanks in advance...

Histologically and embryologically, lips are part of the tegument.  They come
from ectoderm, as does most of the lining of the mouth, and the outer part of
the lip is keratinized stratified squamous epithelium, just like skin but
without hair follicles.  It is thinner than skin and the layers underneath are
highly vascularized so you see the blood underneath, which makes part of the
lip appear red.

The digestive system comes from endoderm.  The digestive system and tegument
meet at the back of the throat, I believe.

Gary Radice
University of Richmond

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