Cow stomach

Cow stomach is very capacious and occupies nearly three-fourths of its abdominal cavity. It is the organ of the cow’s digestive system that divides into larger non-glandular and small glandular compartments.

Here, I will describe the anatomy of the cow’s stomach and practical identification with hand-drawing diagrams and real images.

Quick answer: Cow stomach consists of four compartments (rumen, reticulum, omasum, and abomasum) that fill up most of the abdomen.

I will help you to learn the surface and topographic location of the cow’s stomach. However, you will also learn the external and internal features of the four stomach compartments perfectly.  

What is the stomach in a cow?

Figure 1 presents a hand-drawn schematic of the abdominal cavity, showing various organs and structures. It presents a voluminous organ that covers the largest part of the  cavity and is termed the stomach.

However, it is actually a single stomach that has expanded and divided into various compartments.      

Location of the cow’s stomach

Location: Figure 1 also shows that the cow’s stomach covers the left half of the abdominal cavity. However, a small space is occupied by the spleen and parts of the small intestine.

Extension: The cow’s stomach extends from the seventh rib to the pelvic inlet. However, it remains considerably over the median plane into the right half.

Thus, you may state the location and extension of the cow’s stomach as shown in Table 1 –

Location/extension	Cow’s stomach
Location of the stomach	Left side of the abdominal cavity
Extension of the stomach	7th rib to pelvic inlet

However, you might learn the specific location of every single compartment of the cow’s stomach. I will mention the specific location of the four compartments of the cattle/ox/cow’s stomach while describing the individual.

Compartments or parts of the cow’s stomach

Figure 2 shows four different parts or compartments of the cow’s stomach. The shape, size, and extension of the four compartments are distinctly variable.

Having these four compartments, the cow’s stomach is also known as the compound stomach. Here, Table 2 presents the four parts or compartments of the cow’s stomach –

Compartments of the cow’s stomach	Speciality
Rumen	Larger elongated sac
Reticulum	Smallest part and faces cranially
Omasum	Oval/ellipsoidal shapeFaces the right side of the median plane
Abomasum	Elongated, pyrifom sac-like structureLies on the cranial part of the abdominal floor

Here, the first three compartments (rumen, reticulum, and omasum) are known as the fore-stomach/proventriculi. Sometimes, they are also termed the esophageal sacculation or glandular compartments. However, the last part/compartment (abomasum) of the cow’s stomach is the stomach proper.  

The relative sizes of these four compartments change with the cow’s age. However, stomach capacity is also variable across ages.

Cow stomach anatomy

Figure 3 presents an overview of the external features of the cow’s stomach. It only highlights the main external anatomical features of the rumen, reticulum, omasum, and abomasum.

However, I created this figure of the cow’s stomach using a combination of a hand-drawn diagram and real images. It presents the following features from the rumen compartment –

• Dorsal and ventral sacs of the rumen,
• Caudo-dorsal and caudo-ventral blind sacs of the rumen,
• Right and left longitudinal groove (along with the insula ruminis),
• Dorsal and ventral curvatures of the rumen, and
• Atrium ventriculi and the groove between the rumen and the reticulum,

The figure also identifies the following main external features of the reticulum –

• Parietal and visceral surface of the reticulum,
• Lesser and greater curvatures of the reticulum, and
• Right and left extremities of the cow’s reticulum compartment,

Again, the figure highlights the following external features from the omasum compartment –

• Visceral and parietal surface of the omasum, and
• Dorsal and basal curvatures of the omasum compartment,

Finally, the figure identifies the following external anatomical features from the abomasum compartment –

• Different parts: fundus, body, and pyloric parts,
• Parietal and visceral surfaces of the abomasum, and
• Greater and lesser curvatures of the cow’s abomasum,

However, Figure 4 highlights the most important internal anatomical features of the four compartments of the cow’s stomach. These features are important for identifying and differentiating these four compartments from one another.  

• Rumen: It presents different pillar and carpet-like papillae on the mucous membrane.
• Reticulum: It shows a honeycomb-shaped structure on the mucous membrane.
• Omasum: The interior of the cow’s omasum contains hundreds of longitudinal muscular folds/laminae omasi.
• Abomasum: It shows various oblique mucosal folds, called rugae.

External anatomy of the cow/cattle/bovine rumen

Figure 5 presents the hand-drawing diagrams of the cow’s rumen. It identifies the location, extension, and other features from both the right and left sides of the rumen.

To describe any compartment of the cow’s stomach anatomy, you might describe its surfaces, borders, curvatures, and other external features. However, you might also mention the location, extension, and topographic relationship of the compartment with other organs.

Location and extension of the cow’s rumen

Figure 5 shows that the rumen is the largest and most voluminous compartment of the cow’s stomach. It occupies most of the left half of the abdomen. However, it extends considerably over the median plane to the right side of the abdominal cavity.

Within the abdominal cavity, the rumen extends from the level of the seventh or eighth intercostal space to the pelvic inlet. However, cranially, it is related to the caudal part of the reticulum.

It is somewhat compressed from side to side and presents 2 surfaces, 2 borders, and 2 extremities for description.

Surfaces of the rumen

Figure 6 shows that the rumen has 2 distinct surfaces: the visceral and parietal surfaces. Both surfaces are related to various organs of the abdominal cavity.

Parietal surface: This surface is convex and chiefly related to the diaphragm, the left wall of the abdomen, and the spleen. Thus, the parietal surface of the rumen faces the left side.

Here, the parietal surface of the rumen presents the left longitudinal groove.

Visceral surface: This surface is irregular and related to the omasum, abomasum, liver, and pancreas. However, it has a relationship with the left kidney, left adrenal gland, aorta, and caudal vena cava.

Thus, the visceral surface faces right and also presents the right longitudinal groove. Here, the right longitudinal groove divides into dorsal and ventral branches. However, these branches enclose an elongated swelling, termed the insula ruminis.

Borders/curvatures of the cow/cattle/bovine rumen

Figure 7 highlights the borders or curvatures of the cow’s rumen. It shows two distinct rumen curvatures: dorsal and ventral.

Dorsal curvature: It is convex and follows the curve formed by the diaphragm and sublumbar muscles of the cow’s muscular system. It is firmly attached to the left part of the crura of the diaphragm and sublumbar muscles by peritoneum and connective tissue.

Ventral curvature: It is also convex, and most of its length lies on the floor of the abdomen.

Extremities and sacs of the cow’s rumen

Figure 8 highlights the extremities and various sacs of the cow’s rumen. It presents two extremities: cranial/reticular and caudal/pelvic. However, it also presents the dorsal sac, ventral sac, caudo-dorsal sac, caudo-ventral sac, and atrium ruminis.

Cranial/reticular extremity: It is divided ventrally by a cranial transverse groove into two sacs. Here, the dorsal sac is longer and termed the atrium ruminis (Figure 8).

It continues caudally with the dorsal sac of the rumen and cranially with the reticulum. However, it is rounded and blind, which curves over the ventral sac of the rumen.

The figure also shows that the junction between the atrium ruminis and reticulum is marked by a groove. It is the rumino-reticular groove, which is deep ventrally.

However, the groove is distinct on the lateral surface, but no natural separation exists dorsally. Here, the rumen and reticulum form a dome-shaped structure (atrium ventriculi) on which the cow’s esophagus terminates.

Caudal/pelvic extremity: It extends nearly to the pubis bone of the cow’s hip. However, it is related to the intestine, urinary bladder, and also to the cow’s uterus. The caudal extremity presents a deep caudal transverse groove.

Sacs of the rumen: Previously, you found two longitudinal grooves (left and right) on the parietal and visceral surfaces of the rumen (Figure 6). They actually divide the rumen into two larger sacs: a dorsal and a ventral sac.

However, the caudal transverse grooves on both parietal and visceral surfaces connect with the longitudinal grooves. Thus, they divide the rumen into caudo-dorsal and caudo-ventral blind sacs.

These grooves, also known as coronary grooves, are formed by the vessels (Figure 8).

Internal features of the cow/cattle/ruminant’s rumen

Figure 9 shows the internal anatomical features of the cow’s rumen. It presents different pillars, rumino-reticular folds, the cardia, and larger papillae.

What are the pillars of the cow’s rumen?

The internal cavity of the cow’s rumen is primarily divided into two sacs by the pillars. These are the folds of the ruminal wall that are strengthened by the additional muscular fiber. However, they correspond with the grooves on the external surface of the rumen.

• Cranial pillar: It is an oblique fold at the cranial end of the dorsal and ventral sacs of the rumen. However, it has a thick concave free edge.
• Caudal pillar: It is very thick and separates the caudo-dorsal and caudo-ventral sacs of the rumen. It also possesses a free edge and communicates with two ruminal sacs.    
• Right and left longitudinal pillars: They extend from the corresponding right and left extremity of the cranial pillars. However, these pillars are less prominent than the others.
• Dorsal and ventral coronary pillars: The dorsal and ventral pillars start from the left and right ends of the caudal pillar. However, they extend along the corresponding dorsal and ventral coronary grooves. Thus, they marked the posterior blind sacs from the general cavity or sac of the rumen.
• Accessory pillar: Sometimes, an accessory pillar extends from the dorsal aspect of the right longitudinal pillar.

Rumino reticular folds and cardia

Here, the internal rumino reticular folds correspond to the rumino reticular groove of the external surface. Its free dorsal edge is concave and forms the ventral and lateral margin of the large oval rumino-reticular orifice.

Here, the cardia marks the entry of the esophagus into the rumen. It presents a slit-like opening and is about four to five inches ventral to the vertebral end of the eighth rib.

Papillae of the internal surface of the rumen

The mucous membrane of the rumen is brown except on the margin of the pillar. Here, the majority is thickly studded with larger papillae.

The edges of the main pillars and a large part of the wall of the dorsal sac are non-papillated. However, the papillary arrangements are more developed in the blind sacs.

The papillae of the rumen compartment vary greatly in size and form. Here, the largest are foliate, many are filliforms, and others are conical.

The papillary arrangement of the rumen’s internal surface resembles a carpet.

Cow’s reticulum compartment (external features)

Figure 10, which is the combination of hand-drawing and a real image, highlights the cow’s reticulum. It presents the 2 surfaces, 2 curvatures, and 2 extremities of the cow’s reticulum.

Here, the reticulum is the most cranial and the smallest of the four compartments of cow stomach. However, it is somewhat piriform in shape and is compressed craniocaudally.

Location of the cow’s reticulum

The cow’s reticulum is located between the diaphragm and liver in front and the dorsal sac of rumen and omasum behind. However, it extends from the level of the sixth to the seventh or eighth ribs.

Again, the greater part of the reticulum lies to the left of the median plane. Figure 10 also shows the extension of the cow’s reticulum.

Surfaces of the reticulum

The figure also shows that there are two distinct surfaces in the cow’s reticulum: parietal and visceral. Here, the parietal surface is also called the diaphragmatic surface, whereas the visceral surface is called the ruminal surface.

Parietal/diaphragmatic surface: This surface faces forward and is convex. However, it lies against the concave abdominal surface of the diaphragm and liver.

Visceral/ruminal surface: It faces backward and is flattened by the pressure of the other three compartments. However, it ends dorsally by joining with the wall of the rumen.

The concave line of junction of the rumen and reticulum corresponds to the ridge of the interior. However, this junction forms the lower margin of the rumino-reticular orifice.

Curvatures of the cow’s reticulum compartment

Lesser curvature: Here, the lesser curvature of the cow’s reticulum faces to the right and dorsal (Figure 10). However, it is connected with the omasum compartment of the cow’s stomach.

Greater curvature: Here, the greater curvature of the reticulum faces to the left and ventrally. However, it lies against the diaphragm, opposite to the sixth and seventh ribs.

Extremities of the reticulum

Ventral/right extremity: This extremity of the cow’s reticulum forms the rounded cul-de-sac. It is in contact with the sternal part of the diaphragm, liver, omasum, and abomasum.  

However, the ventral extremity of the reticulum is termed the fundus reticuli. It is opposite to the ventral end of the sixth intercostal space.

Dorsal extremity: Here, the dorsal extremity of the reticulum is connected with the atrium ruminis.

Cow’s reticulum – internal identifying features

Figure 11 presents the interior features of the cow’s reticulum, which are unique among the four compartments. It shows the honeycomb mucous membrane, reticulo-omasal orifice, and esophageal groove.

Honeycomb appearance and papillae: Here, the interior mucous membrane of the reticulum is raised into folds about half an inch high. They enclose four, five, or six-sided spaces or cells.

These spaces are subdivided by smaller fold and their bottoms are studded with the pointed papillae. This peculiar arrangement of the mucous membrane of the reticulum gives it a honeycomb-like appearance.

The spaces grow smaller and gradually disappear near the esophageal groove and edge of the rumino-reticular fold. However, at the rumino-omasal orifice, there is another peculiar type of papillae. These papillae curve and are termed the unguliform papillae.

Reticulo-omasal orifice: The rounded reticulo-omasal orifice is located at the lesser curvature of the reticulum. It is just five to six inches above its bottom. However, it is limited below and laterally by the junction of the lips of the esophageal groove.

Esophageal groove: It begins at the cardia of the rumen and passes ventrally on the internal face of the wall of atrium ruminis. However, it is about seven or eight inches in length and ends at the reticulo-omasal orifice.

This groove is directed dorsoventrally and twisted in a spiral fashion. Its thickening edge projects first caudally, then to the left, and finally cranially.

External anatomy of the cow’s omasum

Figure 12 highlights the exterior anatomical features of the cow’s omasum compartment of its stomach. It is ellipsoidal in form and is somewhat compressed between its parietal and visceral surfaces.

However, the long axis of the cow’s omasum is nearly vertical. Again, it is clearly marked off from other compartments of the cow’s stomach.

Location of the cow’s omasum

Location: Figure 13 shows the exact location of the cow’s omasum in the abdominal cavity. However, it is located almost entirely on the right side of the median plane, opposite the seventh to eleventh ribs (7th – 11th).  

However, it has a close contact with the rumen, reticulum, abomasum, liver, and diaphragm within the abdominal cavity. For description purposes, the cow’s omasum presents 2 surfaces, 2 curvatures, a base, and a neck.

Surfaces of the cow/cattle/bovine omasum

Here, Figures 12 and 13 both present the surfaces of the cow’s omasum. They clearly present two distinct surfaces: parietal and visceral.

Parietal surface: Here, the parietal surface of the cow’s omasum faces to the right and cranially. However, it lies against the diaphragm, liver, and the right lateral wall of the abdomen.

The contact with the latter is limited to a small area. Here, it contacts the ventral part of the eighth, ninth, and tenth ribs only.

Visceral surface: Here, the visceral surface of the cow’s omasum faces left and caudal. It remains in contact with the right surface of the cow’s rumen, reticulum, and abomasum.

Curvatures and neck of the omasum

The above figures also present the curvatures of the cow’s omasum. It shows there are two distinct curvatures in the cow’s omasum: dorsal/greater and ventral/lesser.

Dorsal curvature: The dorsal or greater curvature faces dorsally and somewhat backward. It is convex and related to the diaphragm, liver, and intestine of the cow.

Ventral curvature: The ventral or lesser curvature of the omasum faces ventrally and somewhat forward. It is concave and remains in contact chiefly with the abomasum.

The junction with the abomasum appears as a constriction near the middle of the curvature. However, the ventral curvature is sometimes considered the base of the cow’s omasum.

Neck: The anterior upper part of the ventral curvature is very short, narrow, and called the neck. It connects with the part of the cow’s reticulum.

Interior anatomy of the cow’s omasum

Figure 14 presents the interior anatomy of the cow’s omasum compartment. It shows the laminae omasi, sulcus omasi, and omso-abomasal orifice from the interior surface of the omasum.

Laminae omasi: So, according to the figure, the omasal cavity is occupied by about a hundred longitudinal muscular folds. They actually form the dorsal wall and the sides of the omasum/ curvature. These muscular folds are known as the laminae omasi.

There are ten to twelve larger folds that have a convex attached edge, and a ventral concave free edge. They reach within a short distance of the ventral wall of the cow’s omasal sac.

Sulcus omasi: The ventral wall of the cow’s omasum presents a groove. It connects the reticulo-omasal opening with the omaso-abomasal opening. This groove is the sulcus omasi of the cow’s omasum.

However, the sulcus omasi is a few inches long and directed backward and downward.

Omaso-abomasal orifice: It is an oval structure, four inches long, within the interior part of the omasum. However, it is bounded in front by the thick muscular pillars.

Cow abomasum compartment – external features

Figure 15 highlights the external anatomical features of the cow’s abdomasum. It also presents that the cow’s abomasum has 2 surfaces, 2 curvatures, and 3 parts.

Among the four compartments of the stomach of a cow, the abomasum  is unique in its appearance and function. It is an elongated, pyriform sac whose narrow posterior part is strongly curved, and the concavity is dorsal.

Location of the cow’s abomasum

Location: Most of the cow’s abomasum lies chiefly on the abdominal floor. However, it remains to the right of the reticulum and ventral sac of the cow’s rumen.

Again, the cow’s abomasum extends from the seventh rib to the xiphoid cartilage of the cow’s sternum.

Surfaces of the abomasum

According to Figure 15, there are two distinct surfaces in the cow’s abomasum: parietal and visceral.

Parietal surface: The parietal surface of the cow’s abomasum faces right and lies against the abdominal wall. It extends from the opposite to the 7th /8th ribs to the 11th or 12th costal cartilages.

Visceral surface: Here, the visceral surface of the abomasum is chiefly related to the ventral sac of the rumen.

Curvatures of the cow’s abomasum

The figure also shows that the cow’s abomasum has 2 curvatures: lesser and greater. I will help you to identify and understand these curvatures from the abomasum.

Lesser curvature: Let’s see Figure 15, and it shows a dorsal curve that remains in contact with the omasum. This curve is the lesser curvature of the cow’s abomasum.

However, the junction between the omasum and abomasum is indicated by a constriction. It is located at the anterior extremity of the cow’s abomasum.

Greater curvature: Here, the greater curvature is ventral and rests on the abdominal wall. However, it extends from the xiphoid cartilage to the ventral part of the last intercostal space. Again, its direction is approximately parallel to the right costal arch.

Parts of the bovine abomasum

The above figure also identifies 3 distinct parts: fundus, body, and pyloric.

Fundus part: It is the anterior blind end of the cow’s abomasum. However, it remains at the xiphoid region of the sternum and is chiefly related to the reticulum. It also shows the relationship with the atrium ruminis and the ventral sac of the cow’s rumen.

Body of the abomasum: Here, the intermediate part of the abomasum is termed the body. It extends back between the ventral sac of the rumen and the omasum. However, it turns to the right behind the omasum.

The body part of the cow’s abomasum is constricted in the middle. Thus, it forms the cranial larger part and the caudal pear-shaped smaller part.

Pyloric part: This part of the abomasum inclines dorsally and joins with the duodenum. However, this occurs at the level of the ventral part of the tenth rib in a cow.

Interior of the cow’s abomasum

Figure 16 highlights the interior anatomical features of the cow’s abomasum. It presents 3 glandular areas (fundic, pyloric, and cardiac) and mucosal spiral folds.

Sometimes, it is believed that the abomasal cavity is divided into two distinct areas by a constriction –

First part/fundus: It is lined by a soft, glandular mucous membrane. However, it forms a dozen or more extensive oblique spiral folds. However, these folds extend from the side of the abomasal groove towards the greater curvature and pyloric part.

Second part/pyloric part: It is narrower and a pear-shaped area that presents a brownish color mucous membrane. This mucosa is devoid of folds but wrinkly in appearance and contains pyloric glands.

However, a small cardiac zone surrounds the omaso-abomasal orifice.

Attachments of the cow’s stomach

Figure 17 shows that the dorsal curvature of the rumen attaches to the crura of the diaphragm and sublumbar muscles. This attachment extends from the esophageal hiatus to the fourth lumbar vertebra of the axial skeleton.

However, the bundle of peritoneum extends from the abdominal wall to the rumen and spleen. However, the bundles form the gastrophrenic and splenophrenic ligaments.

Other than these attachments, the parts of the peritoneum have an extensive attachment to the rumen and other parts of the stomach. The visceral layer of the cow’s peritoneum forms the lesser and greater omenta, which attach to the cow’s stomach.

Lesser omentum: It attaches to the lesser curvature of the rumen, base of the omasum, and the lesser curvature of the abomasum.

Greater omentum: Its superficial part has an attachment with the rumen, duodenum, and specifically with the greater curvature of the abomasum. However, its deep portion attaches to the right ruminal groove and blends with the mesoduodenum.

FAQ’s on the cow’s stomach

Conclusion

Thus, the cow stomach is a complex structure consisting of four compartments. Here, the first three compartments (rumen, reticulum, and omasum) are the forestomach, where the fourth one is the stomach proper.

The external and internal anatomical features are unique in these four compartments of the cow’s stomach. However, the anatomy of the cow’s stomach also describes their location, attachment, and relation with other organs.

References

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