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.

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…

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

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.

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

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.

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 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: cecum L R Left parts of large colon. Right parts of large colon.

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

cecocolic fold right ventral colon left ventral colon cecum 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.

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.

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

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.

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.

LT VENT COL LT DORS COL Pelvic flexure

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

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

desc/sigmoidcolon (with teniae)

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

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

duodenojejunal flexure jejunum transv colon desc colon ascnd duod duodenojejunal flexure

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

right dorsal colon jejunum mesocolon of desc/sigmoid colon

Replace coils of small colon….

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

Replace left parts of large colon ventral to jejunal coils…

Replace the cecum.