IVRI Anatomy
A free veterinary anatomy learning platform for B.V.Sc., M.V.Sc., DVM and veterinary medicine students worldwide, developed at the Veterinary Anatomy Section, ICAR-Indian Veterinary Research Institute, Bareilly—covering VCI/MSVE and international university curricula through regional anatomy, histology, embryology, comparative biomechanics, clinical notes, quizzes and revision.
Ruminants are characterized by a massive composite stomach that dominates the left and ventral abdominal cavity. The first three compartments (proventriculi) are non-glandular and lined with stratified squamous epithelium, while the abomasum is glandular and represents the homolog of the simple stomach.
Reticulum: The most cranial compartment, pressed against the diaphragm mainly left of the median plane and under cover of approximately the 6th-8th ribs. Its mucosa has a honeycomb pattern. The ruminoreticular fold partly separates it from the rumen, with which it communicates widely.
Rumen: Occupies the entire left side of the abdominal cavity, from diaphragm to pelvis. Divided by muscular pillars (coronary, longitudinal, accessory) into ventral and dorsal sacs. Site of primary fermentation by microflora generating VFAs. Gas accumulation causes bloat.
Omasum: On the right side, spherical with leaf-like folds (laminae omasi) that trap and squeeze digesta. The omasal canal connects to the abomasum via the omasoabomasal orifice.
Abomasum: The 'true' stomach — glandular, secretes HCl and pepsin. Located on the ventral abdominal floor, right of midline. Can undergo displacement (LDA/RDA) in high-producing dairy cows.
| OX | Four-compartment stomach. Adult rumen capacity and saliva production vary with body size and diet. The reticular/oesophageal groove reflex directs suckled milk toward the abomasum in the calf. |
| HORSE | Simple single-compartment stomach of relatively small capacity (approximately 8-15 L depending on body size and source). Vomiting is extremely difficult because of the powerful cardia/lower oesophageal sphincter, acute oesophageal entry angle and associated anatomy—not because of the pyloric sphincter. The cecum and ascending colon support hindgut fermentation. |
| PIG | Monogastric with a well-developed diverticulum gastri. Gastric ulcers common near pars oesophagea. |
| DOG | Simple stomach. Prone to gastric dilatation-volvulus (GDV) — stomach rotates on its axis, trapping gas. Emergency. |
Explore the hidden mechanics of why structures are present, absent or modified across domestic and wildlife species—and how each anatomical design supports movement, function and clinical practice.
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