The Abdomen
3.4 Abdominal Cavity
Goal: Study the abdominal contents in situ and on isolated (extirpated) viscera from bovine and caprine cadavers.
In situ: First, study the disposition of the greater and lesser omenta before you disturb any viscera. Know the difference between the omental bursa and suprao- mental recess. Next, identify the abdomi- nal organs residing on the left and right sides of the median plane. Know that the combined rumen and reticulum dominate the left flank, pushing most of the organs
Parietal peritoneum
Ox
External and internal abdominal oblique mm. (reflected down) Rib 13
Transversus abdominis
Figure 3.9 Caudal thorax and abdominal flank regions showing the transverse abdominis (TA) muscle and parietal peritoneum: left lateral view. Note the dorsoventral direction of the TA muscle fibers and some of the lumbar spinal nerves running across its surface. The external and internal abdominal oblique (EAO/IAO) muscles are transected and reflected down. Dorsally, the TA muscle is transected and peeled off the transversalis fascia to demonstrate the parietal peritoneum.
External abdominal oblique m.
(covered by tunica flava abdominis)
Rectus abdominis m.
(covered by external lamina of the rectus sheath) Distinct transverse
tendinous intersections Serratus
ventralis m.
(thoracic part)
Subiliac lymph node Serratus dorsalis
caudalis m.
Goat
Spine of lumbar vertebra
Rectus abdominis m.
covered by parietal peritoneum and internal lamina of the rectus sheath Pelvic inlet
Internal abdominal oblique m.
Ox (a)
(b)
Figure 3.10 (a) Goat abdominal wall with cutaneus trunci muscle removed: left lateral view. The ventrally located rectus abdominis (RA) muscle becomes progressively wider as it courses toward the pubic bone but narrows at its point of attachment on the pubic brim (pectin) to give rise to prepubic tendon (not visible). Note the distinct transverse tendinous intersections deep to the external lamina of the rectus sheath. The external lamina of the rectus sheath is formed by fusion of the aponeurosis of the EAO and IAO muscles. (b) The abdominal and pelvic cavities showing insertion of the RA muscle on the pectin and the disposition of the internal lamina of the rectus sheath: cranial view.
to right median plane except for the spleen and fundic part of the abomasum. At the end of this unit watch videos 8 and 9.
On extirpated (isolated) viscera: Study detailed topography of the entire gastro- intestinal tract and the interior of the four chambers of the stomach (reticulum, rumen, omasum, and abomasum). Trace the disposition of the small and large intestines, especially that of the ascend- ing colon. Note some of the differences between the abdominal structures in small and large ruminants (e.g., pancreatic ducts, shape and internal structures of the kidneys).
3.4.1 Dissection Plan
Refer to the dissection plan in Appendix A and watch video 10 on opening the thorax and abdomen. Briefly, remove the thoracic
and pelvic limbs. Open the thoracic and abdominal cavities all at once by folding back the rib cage and the entire abdominal wall cranial to the pelvic limb (Figures 3.11, 3.12, 3.13, 3.14, and 3.15). Study the peritoneal cavity, omenta, and the contents of the abdominal cavity.
3.4.2 Peritoneum
The peritoneum is the serous membrane that lines the walls of the abdominal and pelvic cavities, covers most surfaces of the abdomi- nal organs, and connects abdominal organs together. On the interior of the abdominal wall (TA and RA muscles), the surrounding peritoneum is known as the parietal perito- neum (Figure 3.10b). The part of the perito- neum found on surface of abdominal organs is the visceral peritoneum. The space between the parietal and visceral peritoneum is the peritoneal cavity.
The peritoneal cavity contains no organs but normally has a small amount of serous fluid that allows for friction-free movement of abdominal organs against each other and against the interior of the abdominal wall.
3.4.3 Omentum
Goal: Study the disposition and arrange- ment of the greater and lesser omenta on the left and right flank before disturbing any of the abdominal organs.
The omentum (plural form is omenta) is an extremely fatty and vascular double-layered, serosal sheet of peritoneum that attaches various parts of the stomach to the dorsal body wall or to other organs. It consists of greater and lesser omenta (Figures 3.11, 3.12, and 3.13). The omenta contain fat deposits with amounts that vary between dif- ferent animals.
In fetal development, the greater and lesser omenta are called dorsal and ventral mes- ogastrium, respectively. The dorsal mes- ogastrium suspends the greater curvature of the small and simple primordium of the ruminant stomach to the roof wall of the Box 3.3
During abdominal surgery through the par- alumbar fossa (paralumbar celiotomy), sur- gical incisions may be oriented parallel with the direction of muscle fibers at each level to avoid cutting nerves and muscle fibers more than necessary.
Box 3.4
Rupture of prepubic tendon is reported in cows with heavy belly weight resulting from twin pregnancy, an undesirable and rare situation. The rupture of the prepubic tendon is likely to be more common in mares than in cows.
Box 3.5
The external and internal laminae of the rec- tus sheath have strong holding power and can be sutured during closure of abdominal incisions (paramedian celiotomy) or through the linea alba on the mid-ventral line (recumbent ventral midline celiotomy).
Greater omentum (superficial leaf) Descending duodenum
Abomasum Left liver lobe
Gallbladder Right liver lobe
Greater curvature of abomasum
Cranial
*
Ox
Figure 3.11 Bovine thoracic and abdominal cavities (limbs removed): right lateral view. The greater omentum is composed of a superficial leaf or wall (visible) and a deep leaf or wall (directly deep to the superficial leaf;
not visible in this view). The deep leaf can be exposed by gently lifting up the superficial leaf on the right flank.
Note the line of attachments of the superficial leaf along the greater curvature of the abomasum and the ventral border of the descending duodenum. Trace this leaf ventrally to the abdominal floor where it passes to the left side under the ventral sac of the rumen. On the left side, it attaches to the left longitudinal groove of the rumen (Figure 3.12). The lesser omentum (*) covers the right lateral surface of the omasum and attaches along the lesser curvature of the abomasum, pylorus, and beginning of the duodenum (Figure 3.13).
Dorsal sac
Ventral sac covered by superficial leaf (or layer) of the greater omentum Reticulum
Heart
Spleen Diaphragm
Left lung
Cranial
Ox
Figure 3.12 Bovine abdominal and thoracic viscera (limbs removed) to show the superficial leaf (or wall) of the greater omentum on the left side: left lateral view. Note the attachment of the superficial leaf of the greater omentum on the left longitudinal groove of the rumen passing cranially to the reticulum. Dotted line shows left longitudinal groove.
developing embryo. Following development of the rumen, reticulum, and large part of the abomasum, the dorsal mesogastrium forms the greater omentum.
The ventral mesogastrium suspends the lesser curvature of the developing stomach to the floor of the abdominal cavity of the devel- oping embryo. It forms the lesser omentum following the differentiation of omasum and the remaining part of the abomasum.
The greater omentum has both superficial and deep leaves or walls (Figures 3.12 and 3.13). The superficial leaf of the greater omentum can be identified on the right and left sides of the abdomen. It lies against the floor of the abdominal cavity beneath the ventral sac of the rumen and between the left and right walls of the abdomen. It encloses the ventral sac of the rumen. The deep leaf lies deep to superficial leaf on the right side of the abdomen. It attaches to the right longi- tudinal groove of the rumen and encloses the intestines. You should understand the complex
disposition of the omenta by reading the fol- lowing detailed description along with study- ing relevant figures.
With the help of figures 3.11, 3.13 and 3.14, trace the line of attachments of the superfi- cial leaf of the greater omentum on the right flank. Note that it has a wide area of attach- ments along the greater curvature of the abo- masum, pylorus, and descending duodenum.
Ventrally, it courses down to the abdominal floor (Figure 3.11). It then passes from the right side to the left side of the abdomen under the ventral sac of the rumen. On the left flank, it attaches along the left longitudinal groove of the rumen (Figure 3.12).
To identify the deep leaf, return to the right side and follow the superficial leaf along the ventral surface of the descending duodenum to where it reflects medially upon itself forming the deep leaf. Note that the deep leaf courses ventrally to run below the intestines and then turns medially to attach on the right longitudi- nal groove of the rumen (Figure 3.15a).
Ventral sac of the rumen covered by the
superficial leaf of the greater omentum Abomasum Omasum covered by lesser omentum Lesser omentum Intestines within the supraomental recess
seen through superficial and deep leaves of the greater omentum
Goat Greater omentum:
superficial and deep leaf and omental bursa in between
Figure 3.13 The abdominal cavity of the goat showing the lesser omentum coursing from the visceral surface of the liver to the lesser curvature of the abomasum (dotted line): right lateral view. The omental bursa, between the superficial and deep leaves of the greater omentum, is opened caudally (see also Figure 3.24a).
No organ is present in the omental bursa.
Lesser omentum (“pig’s ear”)
Abomasum
Goat
Greater omentum (superficial leaf)
Lesser omentum (“pig’s ear”)
Abomasum
Goat (a)
(b)
Liver Greater
Omentum (superficial leaf)
Figure 3.14 (a) Abdominal and thoracic cavity of the goat showing what is colloquially known as “pig’s ear” in the lesser omentum: right lateral view. Dotted line shows the location of the lesser curvature of the
abomasum. (b) Lesser omentum “pig’s ear”: right lateral view of isolated bovine abdominal viscera.
Dorsal sac
Ventral sac Abdominal
wall
Peritoneal cavity
Superficial leaf of the greater omentum
Deep leaf of the greater omentum
Omental bursa
Jejunum
Supraomental recess Cecum
Descending duodenum
Spiral colon Ruminal
gas cap Ascending colon:
proximal and distal loops Lumbar vertebra
Goat
(a)
Figure 3.15 (a) Schematic cross-section of the abdominal cavity which illustrates the disposition of the superficial and deep layers of the greater omentum. The omental bursa (enlarged for demonstration purposes) is a paper-thin space between the superficial and deep layers of the greater omentum. The ventral sac of the rumen projects into the omental bursa. The supraomental recess is a sling formed by the deep leaf of the greater omentum. It suspends the intestinal mass. (b) Thorax and abdomen in a goat showing the supraomental recess: right lateral view. Fingers are inserted medial to the superficial and deep leaves of the greater omentum to demonstrate the supraomental recess.
The sling around the intestines formed by the reflection of the deep leaf and its attach- ment along the right longitudinal groove of the rumen is the supraomental recess (Figure 3.15a, b). The cavity created by the supraomental recess is akin to a holding hammock. The supraomental recess sus- pends different segments of the intestines:
jejunum, ileum, cecum, and the spiral part of the ascending colon (Figure 3.15a).
With help of Figure 3.15(b), gently insert your gloved fingers in the supraomental
recess and examine how this recess confines the intestines away from the body wall, a fea- ture touted as helpful in keeping the intes- tines tucked away from surgical incisions made on the right side of the flank.
To demonstrate the omental bursa, gently lift the superficial leaf of the greater omentum with your finger and separate it from the underline deep leaf. The space between the superficial and deep leaves is the omental bursa (Figures 3.13 and 3.15). The bursa communicates with the peritoneal cavity via Box 3.6
The omenta have a unique ability to promote hemostasis and healing because of their pro- nounced angiogenic activity and rich leuko- cyte cellular contents. Because of their ability
to adhere to adjacent structures, they are fre- quently used in abdominal surgery to seal off gastrointestinal defects and promote healing in various types of abdominal surgery.
the epiploic foramen deep to the visceral surface of the liver (Figure 3.16).
Lift up the liver dorsally to identify the epi- ploic foramen (Figure 3.16). The foramen is located between the caudate liver lobe and caudal vena cava dorsally, and the right lobe of the pancreas (mesoduodenum) and the portal vein ventrally. You should be familiar with these boundaries.
To study the lesser omentum in more detail, expose the visceral surface of the liver by lifting the right border dorsally as seen in Figure 3.13. Trace the attachment of the lesser omentum from the visceral sur- face of the liver to the lesser curvature of the abo masum. Additionally, the lesser omentum courses dorsocaudally along the pyloric part of the abomasum and the beginning of the descending duodenum (Figure 3.13).
The lesser omentum covers the right surface of the omasum (Figure 3.13).
A free slip of the lesser omentum has the appearance of an ear of a pig and is colloquially known as the “pig’s ear” (Figure 3.14a, b). The pig’s ear can be used in omen- topexy, and in identifying the abomasum in cases of left abomasal displacement.
3.4.4 Ruminant Stomach
The stomach of ruminants is composed of four complex chambers or compartments:
(i) reticulum, (ii) rumen, (iii) omasum, and (iv) abomasum, from proximal to distal, respectively (Figures 3.17a, b and 3.18a–d).
Identify each of these organs in situ and study the exterior and interior features of each on an extirpated viscera.
The abomasum is the true (glandular) stomach and is like that found in monogas- tric animals (equine and carnivores).
In situ, the rumen dominates the left side of the abdomen (Figure 3.17a, b). The dorsal and
Right kidney Fingers inserted into the
supraomental recess
Greater omentum: superficial and deep layers
Lesser omentum
Goat
Liver
(b) Figure 3.15 (Continued )
ventral sacs are proportionally similar in size in cattle (Figure 3.18a, b). In contrast, the dor- sal sac and ventral sacs are asymmetrical in sheep and goats, with the caudoventral blind sac extending more caudally than the cuado- dorsal blind sac (Figures 3.17a and 3.18c).
The following is a detailed description of each of the four chambers of the stomach.
3.4.4.1 Reticulum
Goal: You should be able to identify the parietal and visceral surfaces of the reticulum. Understand the clinical
significance of the proximity and the close topographic relationship of the reticulum, diaphragm, and heart. In the interior, identify the shape or appearance of the reticular mucosa, the ruminore- ticular fold, cardia, reticular groove, and reticuloomasal orifice.
The reticulum forms the first part of the forestomach (reticulum, rumen, and oma- sum). It is located largely on the left side of the median plane cranial to the rumen, cau- dal to the diaphragm, and dorsal to the xiphoid process of the sternum (Figure 3.17a).
Epiploic foramen Descending duodenum
Mesoduodenum Gallbladder
Cranial
Caudate liver Ox
Figure 3.16 The bovine abdominal cavity: right lateral partial view. The epiploic foramen is seen ventral to caudate process of the caudate lobe of the liver and dorsal to the mesoduodenum. The liver is pulled dorsally to demonstrate the epiploic foramen. Study the complete boundaries of the epiploic foramen from the text.
Box 3.7
The supraomental recess helps keeps the intes- tines away from the incision site in right flank laparotomy (right paralumbar celiotomy).
The omentum provides storage sites for vis- ceral abdominal fat. Clinically, the omentum helps in tissue repair when sutured over surgi- cal wounds (Box 3.5). It readily adheres to sites
of inflammation and provides vascularization and leukocytes for local immune defense.
Omentopexy is a surgical procedure whereby the greater omentum is sutured to the body wall to prevent displacement of organs from their normal position (e.g., left abomasal displacement).
The surface of the reticulum close to the dia- phragm and left lobe of the liver is called the parietal surface. The surface in contact with the rumen is the visceral surface.
The lumen of the reticulum and rumen are more or less continuous with each other, hence the term ruminoreticular compart- ment. The ruminoreticular compartment is
Dorsal sac
Ventral sac Cranial sac*
Spleen Jejunum
Ruminoreticular groove Cranial groove
Heart Cranial
Goat
Abomasum (fundic part) Reticulum
Diaphragm
Caudoventral blind sac Caudal groove Caudodorsal blind sac
Rumen (dorsal sac) Spleen
Rib 13
Rib 8 Left azygos v.
Heart Ox
(a)
(b)
Ventral sac covered by superficial leaf (or layer) of the greater omentum
Figure 3.17 (a) The abdominal and thoracic cavities in a goat cadaver: left lateral view. The rumen, reticulum, and the fundus of the abomasum are the major occupants of the left side of the abdominal cavity with the ruminoreticular compartment dominating most of the left flank in situ. In live animal, the dorsal sac of the rumen occupies the left paralumbar fossa. Note that the fundic part of the abomasum lies between the reticulum and ventral sac of the rumen. * Cranial sac is also called the ruminal atrium. Dotted line, left longitudinal groove. (b) Bovine thoracic and abdominal cavities: left lateral view. The rumen extends from the cardia (8th rib or 7th intercostal space) to the pelvic inlet. The spleen is relatively enlarged in this cadaver and covers the lateral wall of the reticulum.
Dorsal sac Esophagus
Cranial groove
Ventral sac Reticulum
Cranial
Left dorsal coronary groove
Ruminoreticular groove
Caudoventral blind sac Dorsal
Left ventral coronary groove Ox
Caudodorsal blind sac Caudal groove
Reticulo-omasal orifice Dorsal
sac
Ventral sac Caudodorsal
blind sac
Caudoventral blind sac
Esophagus Reticulum Caudal
groove
Cranial groove Ruminal
recess
Rumino reticular groove Right ventral
coronary groove Right dorsal
coronary groove
Cranial Dorsal
Insula
Accessory groove
Ox
Ruminal atrium (cranial
sac) Cranial sacof rumen
(a)
(b)
Figure 3.18 (a) Bovine ruminoreticular compartment: left lateral surface. Dotted line is the left longitudinal groove. The cranial, caudal, left, and right longitudinal grooves encircle the rumen dividing the rumen into dorsal and ventral sacs. The coronary grooves define the caudodorsal and caudoventral blind sacs. (b) Bovine ruminoreticular compartment: right lateral view. Dotted line is the right longitudinal groove. The right longitudinal groove gives off a right accessory groove with a bulge, insula ruminis, in between the two grooves. (c) Goat’s stomach: left lateral view. Note that the caudoventral blind sac extends more caudally than the caudodorsal blind sac. Dotted line is the left longitudinal groove. (d) Goat’s four-chamber stomach: right lateral view. Chambers are the reticulum, rumen, omasum, and abomasum. Dotted line is the right longitudinal groove. (e,f) Schematic illustrations of the left (e) and right (f) views of a goat’s stomach.
Dorsal sac Cranial
groove Esophagus
Caudodorsal blind sac
Caudal groove Reticulum
Cranial
Abomasum:
fundic part Ventral sac Left ventral coronary
groove Goat
Caudoventral blind sac
Caudal groove
Esophagus
Reticulum
Abomasum Dorsal sac
Ventral sac Omasum
Right ventral coronary groove
Cranial Duodenum
Goat (c)
(d) Figure 3.18 (Continued)