1. We examine the gastrointestinal tract of a donkey in dorsal recumbency (on its back) much as one might do this in abdominal surgery. For the exposure that we use in this presentation, the incisions are different and, as the specimen is preserved, the midventral abdominal incision is much larger than it would be were we actually performing the surgery.
Exploration of the viscera would not be markedly different in a horse. See the presentation, “Equine Abdominal Topography”, for review.

3. 2. Cut along transverse axis (at level of last rib).
1. Cut along long axis.
2. Cut along transverse axis (at level of last rib). L R
Starting your dissection…

4. epidermis
subcutaneous c.t.
(superficial fascia)
Separating the skin from the superficial fascia.
dermis

5. The skin is made up of two layers, a superficial epithelial layer, the epidermis, which is thin, and the dermis, which is a much thicker layer of connective tissue on which the epidermis rests.
The epidermis is usually pigmented and probably no more than 100 microns thick.The dermis is the deeper layer of the skin, continuous with the underlying subcutaneous tissue (superficial fascia).
Different from the fairly uniform epidermis, the thickness of the dermis is variable and depends on the area of the body. In the case of the abdomen, the dermis is thin ventrally, perhaps two to four millimeters thick on average, and becomes gradually thicker as the dorsal midline is approached.

6. In freeing the skin from the superficial fascia in the dissection) keep your scalpel with its sharp edge directed toward the skin.

7. Ventral body wall.
At the sternal end of your longitudinal incision, make a stab incision through the ventral body wall
At the sternal end of your longitudinal incision, make a stab incision through the ventral body wall. Go only about ½” deep.

8. Use the blunt end of hemostatic forceps to push through the peritoneum to enter the abdominal cavity.

9. Now put your finger through the hole that you’ve made and lift the abdominal wall away from the viscera.

10. You’re still not through the peritoneum
You’re still not through the peritoneum. You’re looking at the internal lamina of the rectus sheath.

11. Now you’ve carefully cut through the internal lamina and the peritoneum and you’re looking at abdominal viscera. Lifting the body wall away from the viscera, cut along your longitudinal and transverse incisions to expose the viscera.

12. Abdominal viscera exposed:
cecum L R
Left parts of large colon.
Right parts of large colon.

13. large colon, left parts
large colon, right parts
cecum
cecocolic fold

14. cecocolic fold
right ventral colon
left ventral colon
cecum
desc/sigmoid colon
jejunum

15. cecocolic fold.
Lift up on the apex of the cecum to demonstrate the cecocolic fold.

16. cecocolic fold
???
Pull on the apex of the cecum to demonstrate the cecocolic fold. The fold extends from the lateral tenia of the cecum to the right ventral colon.

17. Draw the cecum away from the viscera as shown.
cecocolic fold
???
Draw the cecum away from the viscera as shown.
??? must be the right ventral colon.

18. jejunum ileum cecum ileocecal fold
The cecum is turned back, to the right, to show the ileocecal fold.
ileocecal fold

19. The ileocecal fold extends from the dorsal tenia of the cecum to the ileum. As a matter of definition, the ileojejunal junction is where the ileocecal fold ends.

20. RT VENT COL
RT VENT COL
LEFT VENT COL
LT VENT COL
CECUM
CECUM
Follow the left parts of the large colon caudally. Note that they curve to the right or enter the pelvic inlet. Find the pelvic flexure and draw it out.
Follow the left parts of the large colon caudally. Note that they curve to the right or enter the pelvic inlet. Find the pelvic flexure and draw it out.

21. RT VENT COL
LT VENT COL
CECUM
Follow the left parts of the large colon caudally. Note that they curve to the right or enter the pelvic inlet. Find the pelvic flexure and draw it out.

22. LT VENT COL
LT DORS COL
Pelvic flexure

23. single tenia, mesentery
left vent colon with haustra
left dors colon no haustra

24. coils of jejunum (no teniae)
Pelvic flexure and left parts of the large colon drawn to the right with the cecum out of the body cavity.
left parts of large colon
rt dors col
rt vent col
coils of jejunum (no teniae)
cecum

25. desc/sigmoidcolon (with teniae)

26. View from the right side.
cecum
cecum
Cecum, pelvic flexure, left parts, and a little of the right parts of large colon drawn out of abdomen, right view.
View from the right side.
Pelvic flexure
pelvic flexure

27. From: Anatomie des Pferdes, W. Ellenberger, H. Baum; 1897
From: Anatomie des Pferdes, W. Ellenberger, H. Baum; Verlags- buchhandlung Paul Parey
sternal flexure diaphragmatic flexure
Right Side
Left Side
right ventral colon
left ventral colon
cecum
jejunum
small colon

31. Coils of jejunum moved out of the way to show the ileum joining the base of the cecum.
ileocecal junction

32. Following the jejunum to the duodenojejunal flexure at the cranial end of the duodenocolic fold.
ascending duodenum

33. duodenojejunal flexure
jejunum
transv colon
desc colon
ascnd duod
duodenojejunal flexure

34. coils of small colon leading to the rectum
right dorsal colon
coils of small colon leading to the rectum

35. right dorsal colon
jejunum
mesocolon of desc/sigmoid colon

36. Replace coils of small colon….

37. transv colon
right dorsal colon
right ventral colon
jejunum
cecum
Replace coils of jejunum ventral to coils of small colon…

38. Replace left parts of large colon ventral to jejunal coils…

39. Replace the cecum.