topography of ruminant abdominal viscera

Why is the paralumbar fossa more prominent in the ox than the horse?

The ox has 13 pairs of ribs vs. 18 in the horse, leaving a larger flank area

Why can more abdominal surgery be done through the paralumbar fossa in cattle vs. horses?

The larger, more prominent paralumbar fossa in cattle gives better surgical access

What surgical procedure uses a left flank incision in cattle?

Cesarean section

List the layers of the ruminant abdominal wall from superficial to deep

Skin, superficial fascia (cutaneous trunci m., subiliac lymph node), deep fascia (tunica flava abdominis), muscles (EAO, IAO, TA, transversalis fascia), parietal peritoneum

What is another name for the deep fascia of the abdominal wall in ruminants?

Tunica flava abdominis (yellow abdominal tunic)

What muscles make up the muscular layer of the ruminant abdominal wall?

External abdominal oblique (EAO), internal abdominal oblique (IAO), transversus abdominis (TA)

What lymph node is found in the superficial fascia of the flank?

Subiliac lymph node

What vein runs along the abdominal wall and is called the "milk vein"?

The cranial superficial epigastric vein

Is the ruminant stomach simple or complex?

Complex (composite lining), unlike the simple stomach of horses and dogs

Do ruminants have 4 separate stomachs?

No — they have ONE stomach with 4 chambers

Name the 4 chambers of the ruminant stomach in order of digesta flow

Rumen, reticulum, omasum, abomasum

Which chambers of the ruminant stomach are non-glandular (forestomach/proventriculus)?

Rumen, reticulum, and omasum

Which chamber of the ruminant stomach is glandular?

The abomasum (the only true/glandular stomach)

What is the approximate total capacity of the adult ruminant stomach?

110–235 liters

Which chamber of the ruminant stomach is the largest and first to receive ingesta?

The rumen

Where does the esophagus open in relation to the forestomach chambers?

At the cardia in the reticulum, but its mucosa protrudes to direct food into the cranial ruminal sac

Where is the rumen located in the abdomen?

Fills nearly all of the left side, from the 8th intercostal space to the pelvic inlet; extends slightly to the right of midline

What structures separate the rumen into ruminal sacs?

The ruminal grooves (external grooves lodging neurovascular supply, filled with fat, covered by peritoneum)

Name the ruminal sacs created by the ruminal grooves

Dorsal ruminal sac and ventral ruminal sac

Name the ruminal grooves of the rumen

Left longitudinal groove, right longitudinal groove, cranial transverse groove, caudal transverse groove, coronary grooves

Which groove separates the rumen from the reticulum?

The ruminoreticular groove

What internal structures correspond to the external ruminal grooves?

Ruminal pillars

What is found on the internal surface of the rumen besides pillars?

Ruminal papillae

What clinical procedures are performed via the left paralumbar fossa related to the rumen?

Rumen trocarization, rumenotomy, intraperitoneal injections, cesarean section

How does the rumen differ between small ruminants and cattle regarding the caudodorsal blind sac?

In small ruminants the caudodorsal sac is small with papillae and indistinct pillars; in bovine the dorsal sac has sparse papillae and distinct pillars

Where is the reticulum located?

The most cranial compartment, in the midline (slightly left), from the 6th–8th intercostal space, contacting the diaphragm and lying over the xiphoid cartilage, close to the heart

Describe the interior lining of the reticulum

Intersecting mucosal crests (reticular cells) forming a honeycomb appearance

What are the 3 components of the ruminoreticular compartment?

Ruminoreticular opening, ruminoreticular groove, ruminoreticular fold (U-shaped)

What structure separates the rumen from the reticulum?

The ruminoreticular groove

What is another name for traumatic reticuloperitonitis/pericarditis?

"Hardware disease"

How does hardware disease cause pericarditis?

Sharp metallic objects penetrate the reticulum's cranial wall, then the diaphragm, then the pericardium, causing pericarditis

How does hardware disease cause hepatitis/liver abscess?

Sharp objects penetrate the reticulum's right wall and enter the liver

Why is the reticulum anatomically prone to causing pericarditis when perforated?

Because the reticulum lies close to the heart

What preventive method is used against hardware disease?

Introducing magnets into the reticulum

How can the cranial ruminal sac be differentiated from the reticulum during rumenotomy?

The cranial sac lacks the honeycomb mucosa seen in the reticulum

Why do small ruminants have a lower incidence of traumatic pericarditis than cattle?

They are selective grazers and don't "vacuum" the ground like cattle do

Where is the omasum located?

On the right side, entirely within the intrathoracic part of the abdominal cavity, at the 8th–11th ribs, protruding about 10 cm below the costal arch

What is the clinical significance of omasal impaction?

Pushing on the omasum through the body wall below the costal arch elicits pain

How does omasum size/shape differ between bovine and small ruminants?

In bovine the omasum is larger than the reticulum and "o-shaped"/spherical; in small ruminants it is smaller than the reticulum, has no contact with the body wall, and is bean-shaped

Where is the abomasum located and what is its capacity?

On the right side (7th–11th rib), directly contacting the abdominal floor, capacity 10–20 liters; lies caudal to the reticulum and under the omasum

Why is the abomasum called the "true stomach"?

Because it is the only glandular chamber of the ruminant stomach

What percentage of displaced abomasum (DA) cases are left-sided vs. right-sided?

Left DA (LDA) ~90%, Right DA (RDA) ~10%

Where does a left displaced abomasum (LDA) become lodged?

Between the rumen and the left abdominal wall

Why is right displaced abomasum (RDA) more serious than LDA?

RDA is associated with torsion of the pylorus, which can twist and damage the vagal nerves running along the lesser curvature

What surgical treatments correct displaced abomasum?

Abomasopexy and omentopexy

Where do the vagal trunks run relative to the abomasum?

The dorsal and ventral vagal trunks run along the lesser curvature of the abomasum

What are the components of the ruminant greater omentum?

Superficial layer, deep layer, omental bursa, epiploic foramen, supraomental recess

What connects the omental bursa to the general peritoneal cavity?

The epiploic foramen

What is the supraomental recess?

A V-shaped hammock (intestinal pouch) formed by the deep wall of the greater omentum; closed cranially, open caudally

What normally occupies the supraomental recess?

Intestine (which can leave caudally) and, in advanced pregnancy, the uterus

What is normally contained within the omental bursa?

The intestinal mass

Which stomach chamber is largest in the neonatal ruminant, and why?

The abomasum — it is largest in neonates because milk needs no fermentation

How do the relative proportions of the 4 stomach compartments change from newborn to adult?

The abomasum dominates at birth; with age and forage intake the rumen and reticulum enlarge greatly to become the largest compartments in the adult

What is the gastric (esophageal/reticular) groove and its function in neonates?

A groove-like structure that allows milk to bypass the rumen/reticulum and pass directly from the esophagus to the omasum/abomasum for early digestion

Where is the spleen located in ruminants?

Entirely on the left side, firmly attached to the craniodorsal aspect of the rumen, compressed between the rumen and the left body wall

Does the ruminant spleen have a gastrosplenic ligament?

No

What is the vertical extent of the ruminant spleen?

From the 7th or 8th costochondral junction to the top of the last intercostal space

What shape is the spleen in cattle vs. small ruminants?

Elliptical in cattle; somewhat triangular in small ruminants

What are hemal nodes?

Lymphatic structures with blood circulation only; they receive and filter blood instead of lymph

Where are hemal nodes typically found in ruminants?

Along the great vessels (aorta), mesenteric regions, perineal fat, and subcutaneous tissue

How are hemal nodes distinguished grossly from lymph nodes?

By their dark brown color

How does the rumen affect the position of the liver in ruminants?

The rumen pushes the liver to the right side of the abdomen

Describe the orientation of the liver lobes in ruminants

Right lobe is dorsal, left lobe is ventral

What is the topographic extent of the liver in cattle?

From the ventral third of the 6th intercostal space to the dorsal third of the last intercostal space; rectangular shape

At what intercostal space is the gall bladder related to the abdominal wall in cattle?

9th–10th intercostal space

Where is liver biopsy performed in sheep/goats vs. cattle?

Sheep/goat: 9th–10th ICS; cattle: 11th ICS; slightly above a line from the tuber coxae to the olecranon

Why is liver biopsy easier in ruminants than in some other species?

Because the lungs do not completely overlap the liver in ruminants

What are the parts of the ruminant pancreas?

Left lobe, right lobe (within the mesoduodenum), and the body (joins the two lobes)

What separates the two lobes of the pancreas anatomically?

The pancreatic notch

List the parts of the duodenum in order and their flexures

Cranial part (sigmoid loop, cranial flexure) → descending duodenum (caudal flexure) → ascending duodenum (duodenojejunal flexure)

Where is the jejunum located in ruminants?

Within the supraomental recess

What structures mark the ileum's junction with the cecum?

The ileocecal fold and ileocecal opening

Where are the mesenteric lymph nodes located in ruminants, and how does this differ from dogs/horses?

Along the attached border of the mesojejunum (between the jejunum and outermost coil of the spiral colon) — NOT at the root of the mesentery as in dogs and horses

On which side of the abdomen does the small intestine lie in ruminants?

The right side, within the supraomental recess

Describe the shape and surface features of the ruminant cecum

Straight and cylindrical, with no teniae and no haustra

Which direction does the apex of the cecum point?

Caudally, toward the pelvic inlet

Where is the cecum located in the abdomen?

Dorsally in the supraomental recess, in the right paralumbar fossa

What connects the ileum to the cecum/colon and what structures are found there?

The ileocecal (T-)junction, with the ileal papilla, ileal orifice, and cecocolic orifice

List the parts of the ascending colon in order

Proximal loop, spiral loop, distal loop

What are the three main divisions of the ruminant colon overall?

Ascending colon (proximal loop, spiral loop, distal loop), transverse colon, descending colon

Where is the cecum positioned relative to the colon loops?

At the most right position

Where is the spiral colon positioned relative to other abdominal structures?

At the most left position, to the right of the rumen

What connects the cecum to the spiral colon?

The proximal loop of the ascending colon

What connects the spiral colon to the right colic flexure/transverse colon?

The distal loop of the ascending colon

Why is the spiral colon not visible on gross dissection from the right side?

Because it lies to the left of the mesojejunum

Where does the distal loop of the ascending colon lie, and how is it attached?

Within the duodenal loop; attached to the duodenal loop by the duodenocolic fold

From what view is distension of the ruminant abdominal wall best evaluated?

From the rear (behind the animal)

Describe the surface appearance of the bovine kidney

Externally lobated (12–25 lobes/lobations); the surface divisions are lobes, not lobules; no renal pelvis

Describe the position and mobility of the left kidney in cattle

Pendulous/floating (physiological wandering kidney); pushed by the rumen to the midline, positioned caudal to the right kidney

Where does the hilus of the left kidney lie, and what happens to the left ureter?

The hilus lies dorsally; the left ureter begins in the midline and inclines back to the left side of the body

How do small ruminant kidneys differ from bovine kidneys?

They resemble canine kidneys — smooth and unipapillary (unipyramidal) rather than lobated

What structures are seen in a smooth, unipapillary kidney (small ruminants)?

Renal crest, common renal papilla, area cribrosa, and renal pelvis

How does the pelvic cavity of ruminants compare overall to other species?

Essentially similar, with the same digestive-genital-urinary relations

What accessory genital glands do bulls, rams, and bucks have that dogs lack?

Prostate, ampulla of the ductus deferens, vesicular glands, and bulbourethral glands

Why is the presence of multiple accessory genital glands in male ruminants clinically relevant?

It contrasts with the dog, which lacks these additional accessory glands, and is relevant on rectal palpation