# Abdominal Aorta: Anatomy and Branches The abdominal aorta is the continuation of the descending thoracic aorta that passes through the aortic hiatus of the diaphragm and runs caudally along the dorsal body wall of the abdomen, ending at the aortic bifurcation into the paired common iliac arteries. Its branches are conventionally grouped into unpaired visceral, paired visceral, and paired parietal vessels, and this branching pattern is the anatomical basis for surgery, imaging, and emergency medicine in every domestic species. Knowing this vessel cold matters because it is the single supply line for the entire abdominal viscera and the pelvic limbs. A surgeon ligating a splenic vessel, a radiologist planning a contrast study, and an emergency clinician palpating a femoral pulse after a road traffic accident are all working with the same map. The abdominal aorta artery tree is also where comparative anatomy becomes clinically visible. A dog and a cow share the same fundamental plan, but the branching of the arch of aorta and the pattern of the visceral trunks differ enough that a clinician moving between species must relearn landmarks. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## The Aortic Arch and the Arch of Aorta: Comparative Species Differences The aortic arch (arch of aorta) is the curved segment that connects the ascending aorta to the descending thoracic aorta. Its position and branching pattern are among the most reliable species identifiers in comparative anatomy. In all domestic mammals the arch gives rise to the vessels supplying the head, neck, and thoracic limbs, but the arrangement of those vessels differs across species. ### Dogs and Cats In dogs and cats, the aortic arch gives off a single large vessel, the brachiocephalic trunk. This trunk then divides into the right and left common carotid arteries and the right subclavian artery, while the left subclavian artery arises separately from the arch. The result is a two-vessel pattern from the arch itself: the brachiocephalic trunk and the left subclavian artery. This is the classic carnivore pattern and is the one students should anchor first. A study of the Eurasian otter, a carnivore, confirmed this fundamental pattern: in all 18 animals examined, two major branches emerged directly from the aortic arch, the brachiocephalic trunk and the left subclavian artery [1]. The same study noted that the brachiocephalic trunk branched to the left common carotid and terminated in the right common carotid and right subclavian in 17 of 18 otters, with a bicarotid artery in the remaining case [1]. That single outlier is a useful reminder that even within a species, variation exists. ### Horses and Ruminants In horses and ruminants, the aortic arch gives off a single brachiocephalic trunk that divides into a bicarotid trunk and the right subclavian artery. The bicarotid trunk then splits into the right and left common carotid arteries. The left subclavian artery arises separately from the arch. The key difference from carnivores is the presence of the bicarotid trunk, a shared origin of both common carotid arteries from a single stem. This is the defining feature of the equine and bovine arch. ### Why the Difference Matters The bicarotid trunk in horses and ruminants means that a single ligature or lesion at the base of that trunk can compromise blood flow to both sides of the head. In dogs and cats, the common carotid arteries arise from the brachiocephalic trunk, but the branching is more distal. For a clinician performing a jugular venipuncture, the difference is irrelevant. For a surgeon approaching the thoracic inlet or a radiologist interpreting an angiogram, it is decisive. ### Comparative Table: Aortic Arch Branching Patterns | Species | Vessels arising directly from the aortic arch | Key feature | |--|--|--| | Dog | Brachiocephalic trunk, left subclavian artery | Single brachiocephalic trunk, no bicarotid trunk | | Cat | Brachiocephalic trunk, left subclavian artery | Same as dog, two direct branches | | Horse | Brachiocephalic trunk, left subclavian artery | Brachiocephalic trunk gives a bicarotid trunk | | Cow | Brachiocephalic trunk, left subclavian artery | Brachiocephalic trunk gives a bicarotid trunk | This table summarizes the standard textbook pattern. Individual variation occurs, and the otter study cited above shows that even within carnivores the brachiocephalic trunk can occasionally form a bicarotid artery [1]. ## Passage Through the Diaphragm: The Aortic Hiatus The aorta enters the abdomen through the aortic hiatus, an opening in the diaphragm. This hiatus lies between the two crura of the diaphragm, dorsal to the esophageal hiatus. The aorta passes through this opening along with the azygos vein and the thoracic duct in many species. The hiatus is not a snug ring like the caval opening for the caudal vena cava. It is a slit between muscular crura, which allows the aorta to move with respiration without compression. Once through the hiatus, the vessel is named the abdominal aorta. It runs caudally in the retroperitoneal space, ventral to the vertebral column and dorsal to the parietal peritoneum. Its position is slightly left of midline in most species, a detail that matters when placing a lumbar sympathetic block or interpreting a lateral radiograph. ## The Abdominal Aorta: Course and Termination The abdominal aorta descends along the lumbar vertebrae, giving off branches in a predictable sequence. It ends at the aortic bifurcation, where it divides into the right and left common iliac arteries. In dogs and cats, this bifurcation occurs around the level of the sixth or seventh lumbar vertebra. In horses and cattle, the bifurcation is more cranial, typically around the fifth lumbar vertebra, because the pelvis is oriented differently. The vertebral levels of the major unpaired visceral branches have been mapped in humans using three-dimensional computed tomography angiography. The celiac artery most commonly arises at the T12-L1 disc, the superior mesenteric artery at the middle of L1, and the inferior mesenteric artery at the middle of L3 [2]. The aortic bifurcation is at the lower border of L4 [2]. These human landmarks are useful as a general guide, but veterinary species have their own vertebral relationships that differ with body length and posture. A separate study of 1,174 patients found that the celiac trunk showed the classical pattern in 93.3 percent of cases, the superior mesenteric artery in 97.1 percent, and the inferior mesenteric artery in 98.5 percent [3]. The same study reported significant sex-related differences: females had higher rates of classical patterns for the celiac trunk (96.2 percent vs. 91.7 percent) and the inferior mesenteric artery (99.1 percent vs. 98.1 percent) [3]. These figures come from human imaging, but they establish the principle that variation is real and that the classical pattern is not universal. ## Unpaired Visceral Branches The unpaired visceral branches supply the abdominal digestive organs. They are single vessels that arise from the ventral surface of the aorta and are named for the embryonic gut segments they supply. ### Celiac Artery The celiac artery is the first major unpaired branch. It arises immediately after the aorta passes through the aortic hiatus. In dogs and cats, it is a short trunk that divides into the left gastric, splenic, and hepatic arteries. The hepatic artery supplies the liver, the splenic artery supplies the spleen, and the left gastric artery supplies the stomach. In horses and ruminants, the celiac artery also gives rise to the right gastric and gastroduodenal arteries, and in ruminants it contributes to the blood supply of the forestomachs. The celiac artery is a critical landmark in surgery. During a splenectomy, the splenic artery is ligated close to the spleen, but the surgeon must be aware of the celiac trunk's position to avoid compromising hepatic or gastric flow. In a dog with a splenic mass, the celiac artery may be displaced or encased, which changes the surgical approach. ### Cranial Mesenteric Artery The cranial mesenteric artery (also called the superior mesenteric artery in human anatomy) arises caudal to the celiac artery. It supplies the majority of the small intestine, the cecum, and the ascending and transverse colon. In dogs and cats, it is a large vessel that fans out into a series of jejunal arteries and ileocolic branches. In horses, the cranial mesenteric artery is the site of the classic lesion of verminous arteritis caused by Strongylus vulgaris larvae. The larvae migrate through the arterial wall, causing thrombosis, aneurysm formation, and colic. This is a species-specific clinical entity that every equine clinician must recognize. The distance between the celiac artery and the cranial mesenteric artery is relatively short. In a human cadaver study, the longitudinal distance between the celiac trunk and the superior mesenteric artery was 19.48 millimeters plus or minus 4.41 millimeters [4]. In dogs, the distance is proportionally similar, though the absolute value is smaller. This short interval is why the two vessels are often grouped together as the "cranial abdominal visceral trunks" in surgical anatomy. ### Caudal Mesenteric Artery The caudal mesenteric artery (inferior mesenteric artery) is the smallest of the three unpaired visceral branches. It arises near the termination of the aorta and supplies the descending colon, the rectum, and part of the anal canal. In dogs and cats, it is a slender vessel that anastomoses with branches of the internal pudendal artery. In horses, it supplies the dorsal and ventral colons and the rectum. The caudal mesenteric artery is clinically important in colorectal surgery because its ligation can compromise blood flow to the descending colon, leading to ischemic stricture. A study of 500 computed tomography angiograms found that the median distance from the inferior mesenteric artery to the aortic bifurcation was 3.48 centimeters in females and 3.84 centimeters in males [2]. This distance is the anatomical buffer that allows a surgeon to mobilize the descending colon without compromising the aortic bifurcation. The same study reported that arteries were positioned closer together in females than in males, a statistically significant difference [2]. ## Paired Visceral Branches The paired visceral branches supply the urogenital organs. They arise from the lateral surface of the aorta and are named for the organs they supply. ### Renal Arteries The renal arteries arise from the lateral aspect of the aorta, usually at the level of the second or third lumbar vertebra in dogs and cats. They are large, short vessels that enter the hilus of the kidney. In most domestic species, the right renal artery is slightly longer than the left because the right kidney is positioned more cranially. The renal arteries are end arteries in the functional sense, meaning they have minimal collateral circulation. Occlusion of a renal artery leads to infarction of the segment of kidney it supplies. The number of renal arteries is usually one per kidney, but accessory renal arteries are common. A study of 1,174 patients found that the number of right and left renal arteries was similar between sexes and did not show a significant difference [3]. In dogs, accessory renal arteries are reported in a small percentage of animals and are clinically relevant during nephrectomy or renal transplantation. ### Gonadal Arteries The gonadal arteries are the testicular arteries in males and the ovarian arteries in females. They arise from the aorta caudal to the renal arteries and run obliquely caudally to reach the gonads. In males, the testicular artery passes through the inguinal canal as part of the spermatic cord. In females, the ovarian artery runs in the mesovarium to reach the ovary. The gonadal arteries are small and can be difficult to identify during surgery, but they are important in procedures such as ovariectomy or orchiectomy, where inadvertent ligation can compromise gonadal blood flow. In horses, the testicular artery is particularly long and tortuous, and it is a site of torsion in cases of testicular torsion. In cattle, the ovarian artery is a key landmark in the approach to the ovary during a flank laparotomy. ## Paired Parietal Branches The paired parietal branches supply the body wall. They arise from the dorsal and lateral surfaces of the aorta and are named for the structures they supply. ### Lumbar Arteries The lumbar arteries are a series of paired vessels that arise from the dorsal surface of the aorta. They correspond to the intercostal arteries of the thorax and supply the lumbar muscles, vertebrae, and spinal cord. In dogs and cats, there are typically seven pairs of lumbar arteries. In horses and cattle, the number varies with the number of lumbar vertebrae. The lumbar arteries anastomose with the intercostal arteries cranially and the iliolumbar arteries caudally. They are clinically relevant in cases of aortic thrombosis, where occlusion of the aorta can compromise spinal cord perfusion and lead to ischemic myelopathy. ### Phrenic Arteries The phrenic arteries are the most cranial of the paired parietal branches. They arise from the aorta just caudal to the aortic hiatus and supply the diaphragm. In dogs and cats, the caudal phrenic arteries are the primary supply to the diaphragmatic crura. In horses and cattle, the phrenic arteries are larger and more numerous. The phrenic arteries are important in diaphragmatic surgery and in cases of diaphragmatic hernia, where vascular compromise can lead to ischemia of the diaphragmatic muscle. ## How the Abdominal Aorta Is Studied and Observed ### Physical Examination The abdominal aorta is not directly palpable in most domestic species because it lies deep to the abdominal wall and viscera. However, the femoral pulse is a direct reflection of aortic flow. In a dog or cat, the femoral pulse is palpated on the medial aspect of the thigh. In a horse, the facial artery is often used, but the femoral pulse can be palpated in the groin. In cattle, the coccygeal artery is the preferred site for pulse assessment. A weak or absent femoral pulse suggests aortic occlusion, severe hypovolemia, or thromboembolism. ### Imaging Radiography can show the aorta as a soft tissue opacity dorsal to the abdomen on a lateral view. Contrast angiography is the traditional method for visualizing the abdominal aorta and its branches. Computed tomography angiography (CTA) is now the standard for detailed vascular mapping. A study of 500 CTA images demonstrated the utility of three-dimensional reconstruction for determining the vertebral positions of the unpaired visceral branches and their distances from each other and from the aortic bifurcation [2]. In [veterinary medicine](/blog/careers/veterinary-medicine-careers-from-clinical-practice-to-public-health), CTA is used for preoperative planning in cases of portosystemic shunts, adrenal tumors, and aortic thrombosis. Ultrasound is a practical tool for assessing the abdominal aorta in real time. The aorta is visualized as a tubular structure with a hyperechoic wall and an anechoic lumen. Doppler ultrasound can measure flow velocity and detect turbulence or thrombosis. In a dog with a suspected aortic thromboembolism, ultrasound can confirm the diagnosis by showing a filling defect in the aortic lumen. ### Surgical Anatomy The abdominal aorta is the reference point for many surgical approaches. During a lumbar sympathetic block, the needle is advanced toward the aorta, and the drug is deposited in the retroperitoneal space. During a celiac artery ligation for a bleeding gastric ulcer, the surgeon must identify the celiac trunk and its branches. During a nephrectomy, the renal artery and vein are ligated close to the hilus. Each of these procedures depends on a precise mental map of the abdominal aorta arteries. ## Clinical Relevance, Limitations and Common Mistakes ### Clinical Relevance The abdominal aorta is central to [veterinary emergency medicine](/knowledge/veterinary-medicine/emergency-critical-care/veterinary-emergency-critical-care-core-competencies-training-pathways). Aortic thromboembolism is a common complication of [feline cardiomyopathy](/knowledge/veterinary-medicine/clinical-methods/feline-cardiomyopathy-types-diagnosis-management), particularly in cats with hypertrophic cardiomyopathy. The thrombus typically lodges at the aortic bifurcation, causing acute hindlimb paralysis, pain, and absence of femoral pulses. This is a true emergency with a guarded prognosis. In dogs, aortic thrombosis is less common but can occur with hyperadrenocorticism, protein-losing nephropathy, or neoplasia. The abdominal aorta is also relevant in trauma. A dog hit by a car can suffer aortic rupture, leading to fatal hemorrhage into the retroperitoneal space. A horse with a pelvic fracture can lacerate the internal iliac artery, a branch of the aorta, causing severe hemorrhage. In cattle, aortic rupture is a recognized complication of copper deficiency, which weakens the aortic wall. In surgery, the abdominal aorta is the landmark for the celiac, cranial mesenteric, and caudal mesenteric arteries. A surgeon performing a colorectal resection must know the distance from the inferior mesenteric artery to the aortic bifurcation to avoid ischemic complications. A study of 500 CTA images found that this distance was 3.48 centimeters in females and 3.84 centimeters in males [2]. This is a useful reference for surgical planning, though species differences must be considered. ### Limitations The anatomical descriptions in this article are based on standard veterinary anatomy and comparative studies. Individual variation is common. A study of 1,174 patients found that the classical branching pattern of the celiac trunk was present in 93.3 percent of cases, meaning that 6.7 percent had a variant [3]. In veterinary species, similar variation occurs. A dog may have an accessory renal artery, a horse may have an aberrant celiac branch, and a cat may have a bicarotid artery. These variants are clinically significant during surgery and imaging. The vertebral landmarks described in human studies are not directly transferable to veterinary species. A dog has 13 thoracic and 7 lumbar vertebrae, while a horse has 18 thoracic and 6 lumbar vertebrae. The absolute level of the celiac artery and aortic bifurcation differs accordingly. Clinicians should rely on species-specific anatomy rather than extrapolating from human data. ### Common Mistakes The most common mistake is confusing the cranial mesenteric artery with the celiac artery. The celiac artery is the first branch and supplies the stomach, liver, and spleen. The cranial mesenteric artery is the second branch and supplies the small intestine and colon. In a dog with a gastric dilation-volvulus, the celiac artery may be compressed, but the cranial mesenteric artery is usually spared. In a horse with colic, the cranial mesenteric artery is the prime suspect for verminous arteritis. Another mistake is assuming that the aortic bifurcation is at the same vertebral level in all species. In dogs and cats, it is around L6 or L7. In horses and cattle, it is around L5. This difference matters when interpreting radiographs or planning a surgical approach to the pelvic limbs. A third mistake is underestimating the clinical significance of the phrenic arteries. These small vessels supply the diaphragm, and their compromise can lead to diaphragmatic weakness or hernia formation. In a dog with a diaphragmatic hernia, the phrenic arteries may be stretched or torn, leading to ischemia of the diaphragmatic muscle. ## Quick Review 1. The abdominal aorta enters the abdomen through the aortic hiatus and ends at the aortic bifurcation into the common iliac arteries. 2. Unpaired visceral branches: celiac artery, cranial mesenteric artery, caudal mesenteric artery. 3. Paired visceral branches: renal arteries, gonadal arteries. 4. Paired parietal branches: lumbar arteries, phrenic arteries. 5. Dogs and cats have a single brachiocephalic trunk and a separate left subclavian artery from the aortic arch. 6. Horses and ruminants have a bicarotid trunk arising from the brachiocephalic trunk. 7. The celiac artery is the first major branch and supplies the stomach, liver, and spleen. ## Frequently Asked Questions ### What is the abdominal aorta? The abdominal aorta is the portion of the descending aorta that runs through the abdomen after passing the aortic hiatus of the diaphragm. It ends at the aortic bifurcation into the common iliac arteries. ### What are the unpaired visceral branches of the abdominal aorta? The unpaired visceral branches are the celiac artery, the cranial mesenteric artery, and the caudal mesenteric artery. They supply the digestive organs. ### How does the aortic arch differ between dogs and horses? Dogs have a single brachiocephalic trunk and a separate left subclavian artery. Horses have a brachiocephalic trunk that gives rise to a bicarotid trunk, which then splits into the right and left common carotid arteries. ### What is the clinical significance of the aortic bifurcation? The aortic bifurcation is the site where the aorta divides into the common iliac arteries. It is a common location for thromboembolism in cats with heart disease, causing hindlimb paralysis. ### What are the paired parietal branches of the abdominal aorta? The paired parietal branches are the lumbar arteries and the phrenic arteries. They supply the body wall and diaphragm. ### Why is the cranial mesenteric artery important in horses? The cranial mesenteric artery is the site of verminous arteritis caused by Strongylus vulgaris larvae. This condition can cause colic and thrombosis in horses. ## Related Articles - [Branches of Biology](/blog/careers/branches-of-biology) - [Abdominal Radiographic Positioning and Normal Anatomy in Small Animals](/knowledge/veterinary-medicine/diagnostic-imaging/abdominal-radiographic-positioning-normal-anatomy-small-animals) - [Abdominal Radiography in Exotic Pets: Indications and Interpretation](/knowledge/veterinary-medicine/diagnostic-imaging/abdominal-radiography-exotic-pets-indications-interpretation) - [Pet Ultrasound Diagnostics: Echocardiogram vs Abdominal Scans Explained](/knowledge/veterinary-medicine/at-home-diagnostics/pet-ultrasound-diagnostics-echocardiogram-vs-abdominal-scans-explained) - [Abdominal Ultrasound in Cats: Normal Findings and Common Abnormalities](/knowledge/veterinary-medicine/diagnostic-imaging/abdominal-ultrasound-cats-normal-findings-common-abnormalities) - [Ultrasonography of the Equine Abdomen: Indications and Findings](/knowledge/veterinary-medicine/diagnostic-imaging/ultrasonography-equine-abdomen-indications-findings) - [Vertebral Artery: Course, Branches, and Clinical Relevance](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/vertebral-artery-course-branches-and-clinical-relevance) ## Further Reading - [Unilateral versus bilateral antegrade cerebral perfusion during aortic arch surgery: an updated meta-analysis of comparative studies.](https://pubmed.ncbi.nlm.nih.gov/41145846/) - [A Multicenter Comparative Study on Two Techniques for Creating Multifenestrated Physician-Modified Stent Grafts in the Treatment of Aortic Arch Pathologies.](https://pubmed.ncbi.nlm.nih.gov/40650357/) ## Sources 1. [Morphology of aortic arch branching patterns in the Eurasian Otter (Lutra lutra, Linnaeus, 1758).](https://pubmed.ncbi.nlm.nih.gov/36792211/) 2. [Determination of vertebral levels and distances between unpaired visceral branches of abdominal aorta using three-dimensional multi-detector computed tomography angiographies.](https://pubmed.ncbi.nlm.nih.gov/42189239/) 3. [Anatomical Variations in Major Abdominal Aortic Branches and Sex-Related Differences: A Large-Scale Analysis of 1174 Patients.](https://pubmed.ncbi.nlm.nih.gov/42042939/) 4. [Intraluminal morphometric analysis of abdominal aortic branches: spatial landmarks for interventional radiology and colorectal surgery.](https://pubmed.ncbi.nlm.nih.gov/42618674/)