原坑

原坑是原結中央的凹陷處。與未來脊索相連接，屬於原線的一部份（原線最末端）。

外部連結 

 http://www.embryology.ch/anglais/hdisqueembry/triderm01.html 
 https://web.archive.org/web/20080809142409/http://isc.temple.edu/marino/embryology/EMBII97/img020.GIF
 http://cancerweb.ncl.ac.uk/cgi-bin/omd?primitive+pit
 https://web.archive.org/web/20070908045428/http://embryology.med.unsw.edu.au///Medicine/BGDlab3_11.htm
 https://web.archive.org/web/20060925080426/http://www.ana.ed.ac.uk/database/humat/notes/embryo/ectoderm/primstr.htm

發育生物學
胚胎學