3. The digestive tract is a long, continuous tube of varying diameter extending from the lips to the anus. It includes oral cavity,esophagus, stomach, small intestines, large intestine and appendix. The oral cavity The oral cavity is lined by mucosa. There are a tongue and 32 permanent teeth in the oral cavity.

4. Fig ． 1 ．

5. Fig ． 2 ．

6. Except the oral cavity, the wall of the digestive tract consists of four layers: mucosa, submucosa, muscularis and adventitia. The mucosa consists of epithelium, lamina propria and muscularis mucosa.

7. Fig ． 3 ． Cross section of esophagus(HE stain,low mag.) Tunica muscularis submucos a mucosa

8. Fig ． 4 ． Stomach (HE stain,low mag.) mucos a submucos a Tunica musculari s

9. Fig ． 5 ． Stomach(HE stain,high mag.) Gastric pit Gastric gland

10. Parietal cell Neck mucous cell Fig ． 6 The mucosa of gastric fundus : fundic glands

11. Fig 7 ． Parietal cell Active cell Resting cell

12. Fig ． 8 parietal cell

13. Chief cells Fig ． 9 The mucosa of gastric fundus : fundic glands

14. Fig ． 10 Chief cell ZG: Zymogen granules

15. The small intestines include duodenum, jejunum and ileum. There are plica circulares and villi on the mucosa of the small intestines.

16. Villus Fig ． 11 Small intestine (jejunum)

18. Striated border Fig ． 12 Villus of small intestine(HE stain,high mag.) Central lacteal Goblet cell Columnar cell

19. Fig ． 13 Villus of small intestine(HE stain,high mag.) Central lacteal Striated border

20. Fig ． 14 absorptive cell

21. Fig ． 15 small intestine gland Paneth cell: acidophilic granules

22. Fig ． 16 Paneth cell: Secretory granules

23. Fig ． 11 Longitudinal section of Colon(HE stain,low mag.) Tunica muscularis mucosa submucosa

24. Intestinal gland epithelium Fig 12 Mucosa of Colon (HE stain,high mag.)

25. Fig 13 Mucosa of Colon (HE stain,high mag.) Intestinal gland

26. Fig ． 14 Cross section of appendix(HE stain,low mag.) Arrowhead:lymphoid nodule Intestinal gland muscularis mucosa