THE PHARYNX AND STOMATODAUM. oo 
The fore-gut, a relatively wide space, continuous posteriorly with the mid-cut 
is thus at first closed anteriorly by the bucco-pharyngeal membrane, which separates 
it from the stomatodeum. About the fifteenth day, in the human embryo, the bueco- 
pharyngeal membrane disappears, the fore-gut is then thrown into continuity 
with the stomatodeal space, and the anterior opening of the alimentary canal 
is formed. Z 
As development proceeds the cavity of the fore-gut is gradually compressed 
dorso-ventrally, until its transverse section assumes a triangular outline; but in 
the earliest stages there are no indications of the various organs which are ulti- 
mately developed from its walls. After a short interval, however, two elevations 
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30N Eom 2s 
Fic. 27. FURTHER DEVELOPMENT OF THE ALIMENTARY CANAL, AS SEEN IN A HUMAN EMBRYO 
ABOUT FivE WEEKS OLD (Diagrammatic). 
The tongue is well formed, the trachea and esophagus are separated, the bronchi have commenced to branch ; 
the duodenal curve is well formed, and the cecum has appeared in the loop of the mid-gut. The 
cloaca is partially separated into genito-urinary and rectal portions. 
1. Hind-brain. 7. Trachea. 13. Pancreas. 19. Vertebra. 25. Rectum. 
2. Mouth. 8. Gisophagus. 14. Small intestine. 20. Spinal cord. 26. Proctodeum. 
3. Tongue. 9. Lung. 15. Caecum. 21. Bladder, 27. Allantoic diverticulum. 
4. Pericardium. 10. Liver. 16. Intestinal loop. 22. Wolffian duct. 28. Vitello-intestinal duct. 
5. Pharynx. 11. Bile duct. 17. Large intestine. 23. Kidney. ; 29. Fore-brain. 
6. Heart. 12. Stomach. 18. Notochord. 24. Ureter. 30. Mid-brain. 
appear in its ventral wall. The anterior of these is a rounded elevation, termed 
the tuberculum impar. It is situated directly behind the lower ends of two raised 
bars or arches, called the mandibular arches, which are growing down into the floor 
of the fore-gut from the anterior parts of its lateral walls. The tuberculum impar 
is the rudiment of the anterior two-thirds of the tongue, which is thus formed in 
the floor of the entodermal portion of the alimentary canal. The more posterior 
elevation, termed the furcula, is a curved ridge, which bounds a mesial longitudinal 
depression. It is separated from the lateral walls of the fore-gut and from the 
tuberculum impar by a groove, the sinus arcuatus. The anterior part of the fureula 
is transformed into the epiglottis and the margins of the upper aperture of the 
larynx; the median depression becomes the cavity of the larynx and of the trachea. 
Still more posteriorly, behind the region of the furcula, a dilatation of the fore-gut 
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