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.

R L

1. Cut along long axis.

2. Cut along transverse axis (at level of last rib).

epidermis

dermissubcutaneous c.t.

(superficial fascia)

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.

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

Ventral body wall.

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

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

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

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.

Abdominal viscera exposed:

RL

cecum

Left parts of large colon.

Right parts of large colon.

cecu

m

large colon, left parts

large colon, right parts

cecocolic fold

left ventral colon

right ventral colon

cecu

m

desc/sigmoid colon

jejunum

cecocolic fold

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

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.

cecocolic fold

???

Draw the cecum away from the viscera as shown.

cecocolic fold

???

??? must be the right ventral colon.

cecum

ileocecal fold

ileum

jejunum

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

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.

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.

CECUM

RT VENT COL

LT VENT COL

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.

RT VENT COLLEFT 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.

CECUM

RT VENT COL

LT VENT COL

Pelvic flexure

LT VENT COL

LT DORS COL

left vent colon with haustra

left dors colon no haustra

single tenia, mesentery

Pelvic flexure and left parts of the large colon drawn to the right with the cecum out of the body cavity.

cecum

coils of jejunum (no teniae)

rt dors col

rt vent col

left parts of large colon

desc/sigmoidcolon (with teniae)

View from the right side.Pelvic

flexure

cecumCecum, pelvic flexure, left parts, and a little of the right parts of large colon drawn out of abdomen, right view.

pelvic flexure

cecum

Right Side Left Side

right ventral colon

left ventral colon

cecum

jejunum

sternal flexure diaphragmatic flexure

From: Anatomie des Pferdes, W. Ellenberger, H. Baum; 1897. Verlags- buchhandlung Paul Parey

small colon

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

ileocecal junction

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

ascending duodenum

jejunum

duodenojejunal flexure

transv colon

desc colonascnd

duod

jejunum

coils of small colon leading to the rectum

right dorsal

colon

mesocolon of desc/sigmoid colon

right dorsal colon jejunum

Replace coils of small colon….

Replace coils of jejunum ventral to coils of small colon…

cecum

right ventral colon

right dorsal colon

jejunum

transv colon

Replace left parts of large colon ventral to jejunal coils…

Replace the cecum.