Greater omentum [Epiplon]

The greater omentum is a large, apron-like fold of visceral peritoneum that extends from the greater curvature of the stomach and the proximal part of the duodenum, draping over the intestines (primarily the small intestines), and then turns dorsally to attach to the dorsal body wall, typically near the pancreas or the dorsal mesogastrium. It consists of a double-layered peritoneal fold, often referred to as having a superficial and a deep leaf, forming a closed sac in many species.

2. Composition and Layers

• Superficial leaf: Runs ventrally from the greater curvature of the stomach and the initial portion of the duodenum.

• Deep leaf: Turns dorsally and ascends to the dorsal abdominal wall, enclosing the omental bursa, a potential space between the two leaves.

• The omentum is highly vascularized and contains lymphatics, fat deposits, and immune cells.

3.Parts and ligaments

The greater omentum is subdivided into different parts or extension, termed as "ligaments" that connect it to adjacent structures:

• Gastrophrenic ligament

• Gastrosplenic ligament [Gastrolienal ligament]

• Phrenicosplenic ligament

• Splenorenal ligament [Lienorenal ligament]

• Omental veil

4. Species Differences

Canine (Dog)

• The greater omentum is extensive and easily identifiable.

• It covers the entire ventral surface of the abdominal viscera.

• It provides mechanical protection and helps in immune surveillance and fat storage.

Feline (Cat)

• Similar to dogs but less voluminous.

• Still covers the ventral abdominal organs prominently.

Equine (Horse)

• Less developed compared to carnivores.

• It does not extend as far caudally and doesn’t envelop the intestines as extensively.

Ruminants (Cattle, Sheep, Goats)

• Exceptionally large and complex.

• Forms a superficial and deep leaf that create a large supraomental recess, housing most of the intestines.

• In cattle, the greater omentum attaches to the rumen, specifically the longitudinal groove.

• Plays a major role in localizing abdominal infections due to its size and immune activity.

Swine (Pig)

• Intermediate in development.

• Covers the abdominal organs to some extent but not as extensively as in dogs or ruminants.

5. Functions

• Mechanical protection: Cushions abdominal organs against external trauma.

• Immune surveillance: Contains macrophages and milky spots for immune responses.

• Fat storage: Especially important in carnivores and ruminants.

• Infection containment: Localizes peritonitis or intra-abdominal abscesses.

• Wound isolation and healing: Wraps around inflamed or injured areas.