Science Friday - Halloween Edition

Happy Friday and Happy Halloween! Here is the next installment of Guess the Body Part. These two pictures are of the same thing. The top one is a cross section of the structure that has been stained with haematoxylin and eosin.  The bottom picture was taken using a scanning electron microscope. Ok, send me your guesses (and remember, this is the Halloween Edition - hint, hint).

Disclaimer - I didn't take either one of these pictures.