Subclavian Artery: Anatomy and Branches

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

The subclavian artery is the paired major vessel that supplies the thoracic limb, the ventral neck, the thoracic wall, and part of the central nervous system, running from its origin near the thoracic inlet to the outer border of the first rib, where it becomes the axillary artery. Its branches, including the vertebral artery, internal thoracic artery, thyrocervical trunk, costocervical trunk, and dorsal scapular artery, form the vascular scaffolding for the shoulder, neck, and cranial mediastinum.

For veterinary students, the subclavian artery is a crossroads. It is where comparative anatomy, embryology, and clinical imaging meet. The same vessel that feeds a dog's forelimb also gives rise to the vertebral artery that perfuses the brainstem and cerebellum, and its branching pattern varies enough between dogs, cats, and humans that a single memorized diagram will mislead you. Understanding the subclavian artery means understanding not just where the blood goes, but why the pattern differs across species and why those differences matter when you interpret an angiogram or plan a surgical approach.

Orientation: What the Subclavian Artery Is and Where It Sits

The subclavian artery is defined by its boundaries. It begins at its origin from the brachiocephalic trunk (in most domestic mammals) or directly from the aortic arch (in humans on the left side), and it ends at the outer border of the first rib, where it continues as the axillary artery. Everything between those two landmarks is subclavian.

In humans, the right subclavian artery arises from the brachiocephalic trunk, while the left subclavian artery arises directly from the aortic arch as its third branch [1]. This asymmetry is a human feature. In dogs and cats, the pattern is different: the brachiocephalic trunk gives off both subclavian arteries, and the aortic arch itself typically has only two major branches, the brachiocephalic trunk and the left subclavian artery, depending on species and individual variation.

The subclavian artery is not a single straight tube. It arches over the pleural dome, passes between the anterior and middle scalene muscles (in humans) or their homologues, and descends toward the axilla. Along the way it gives off branches that supply the neck, thoracic wall, and brain. The vessel's relationships, to the brachial plexus, the pleura, the first rib, and the vertebral column, determine both its vulnerability and its surgical accessibility.

The Three Parts of the Subclavian Artery (Human Model)

Human anatomy textbooks divide the subclavian artery into three parts based on its relationship to the anterior scalene muscle. This framework is useful for understanding branch order, and it provides a reference point for comparing domestic species.

First Part: Medial to the Anterior Scalene Muscle

The first part of the subclavian artery extends from its origin to the medial border of the anterior scalene muscle. It gives off three branches:

• Vertebral artery: Ascends through the transverse foramina of the cervical vertebrae and enters the skull to supply the brainstem, cerebellum, and posterior cerebral circulation. In humans, the vertebral artery typically arises from the first part of the subclavian artery, though variant origins are well documented [2][3].
• Internal thoracic artery: Descends behind the sternum and costal cartilages, giving off anterior intercostal branches and perforating branches to the chest wall and mammary tissue. In humans, it is commonly used as a coronary bypass conduit, which is why subclavian stenosis can cause coronary steal [4].
• Thyrocervical trunk: A short trunk that divides into the inferior thyroid artery, suprascapular artery, and transverse cervical artery. These supply the thyroid gland, the infrahyoid muscles, and the muscles of the scapular region.

Second Part: Behind the Anterior Scalene Muscle

The second part of the subclavian artery lies directly behind the anterior scalene muscle. It typically gives off one branch:

• Costocervical trunk: Divides into the deep cervical artery and the supreme intercostal artery. The deep cervical artery supplies the deep muscles of the neck, and the supreme intercostal artery supplies the first two intercostal spaces.

Third Part: Lateral to the Anterior Scalene Muscle

The third part of the subclavian artery extends from the lateral border of the anterior scalene muscle to the outer border of the first rib. It gives off one branch:

• Dorsal scapular artery: Descends along the medial border of the scapula and supplies the rhomboid muscles and the levator scapulae. In some individuals, the dorsal scapular artery arises from the transverse cervical artery rather than directly from the subclavian artery.

This three-part framework is a human anatomical convention. It is useful for organizing branch order, but it does not map cleanly onto the anatomy of dogs and cats, where the scalene muscles and the branching pattern differ.

Branches of the Subclavian Artery: Summary Table

This table reflects the human pattern. In dogs and cats, the branch order and the presence or absence of specific trunks vary, and the next section explains how.

Comparative Anatomy: Subclavian Artery in Dogs and Cats

The subclavian artery in domestic mammals follows the same general plan as in humans, but the details differ in ways that matter for anatomy exams and clinical imaging.

Origin and the Brachiocephalic Trunk

In dogs and cats, the brachiocephalic trunk is the first major branch of the aortic arch. It gives off the right and left subclavian arteries, as well as the common carotid arteries. This means that in a dog, both subclavian arteries arise from a common trunk, unlike the human pattern where the left subclavian artery arises directly from the aortic arch. The brachiocephalic trunk in dogs is short and wide, and it divides into the right subclavian artery, the left subclavian artery, and the bicarotid trunk (which then divides into the left and right common carotid arteries).

In cats, the pattern is similar, though the brachiocephalic trunk may give off the left subclavian artery separately from the right. The key point is that in both species, the subclavian arteries arise from the brachiocephalic trunk rather than directly from the aortic arch, except in variant anatomy.

The Vertebral Artery

The vertebral artery in dogs and cats arises from the subclavian artery, typically from its first part, and ascends through the transverse foramina of the cervical vertebrae. In dogs, the vertebral artery is a significant contributor to the blood supply of the brainstem and cerebellum, and it is often the target of imaging studies when vertebral artery anomalies are suspected. In cats, the vertebral artery is smaller relative to the carotid system, and the external carotid artery and its branches play a larger role in cerebral perfusion.

The origin of the vertebral artery from the subclavian artery is the norm, but variant origins are well documented in humans and are increasingly recognized in veterinary medicine. In a study of 150 vertebral arteries in humans, 95.3% arose from the subclavian artery, 2.7% from the aortic arch, and the parent vessel was not recorded in 2.0% [2]. In another study of 203 patients, the right vertebral artery arose from the right subclavian artery in 99.5% of cases, with one case of anomalous origin from the right common carotid artery [3]. These variants are relevant to veterinary anatomy because similar patterns can occur in dogs and cats, and they complicate the interpretation of vascular imaging.

The Thyrocervical Trunk

The thyrocervical trunk is a short, wide trunk that gives off the inferior thyroid artery, the suprascapular artery, and the transverse cervical artery. In dogs, the thyrocervical trunk is present but its branches may arise independently from the subclavian artery. In cats, the thyrocervical trunk is often absent as a distinct structure, and the inferior thyroid artery, suprascapular artery, and transverse cervical artery arise directly from the subclavian artery.

A cadaveric study of a 71-year-old human donor reported unilateral absence of the thyrocervical trunk, with the inferior thyroid artery originating from a thyrovertebral trunk and the transverse cervical artery completely absent [5]. This level of variation is relevant to veterinary anatomy because it shows that the thyrocervical trunk is not a fixed structure. In dogs and cats, the same principle applies: the branches of the thyrocervical trunk may arise independently, and the trunk itself may be absent.

The Costocervical Trunk

The costocervical trunk in dogs and cats gives off the deep cervical artery and the supreme intercostal artery. In dogs, the costocervical trunk is a consistent branch of the subclavian artery, and it supplies the deep muscles of the neck and the first two intercostal spaces. In cats, the costocervical trunk is present but may be smaller, and its branches may arise separately.

The costocervical trunk is clinically relevant because it contributes to the collateral circulation of the neck and thoracic wall. In cases of subclavian artery stenosis or occlusion, the costocervical trunk can provide an alternative route for blood flow to the forelimb and thoracic wall.

The Internal Thoracic Artery

The internal thoracic artery in dogs and cats descends behind the sternum and gives off the ventral intercostal arteries and the perforating branches to the mammary glands. In dogs, the internal thoracic artery is a major supplier of the cranial epigastric artery, which continues caudally to supply the rectus abdominis muscle. In cats, the internal thoracic artery is smaller but follows the same general course.

The internal thoracic artery is clinically important because it is used as a conduit in coronary artery bypass grafting in humans, and subclavian stenosis can cause coronary-subclavian steal syndrome [4]. In veterinary medicine, the internal thoracic artery is less commonly used as a bypass conduit, but it remains an important vessel for understanding thoracic wall perfusion and mammary gland blood supply.

The Dorsal Scapular Artery

The dorsal scapular artery in dogs and cats arises from the subclavian artery or from the transverse cervical artery. It descends along the medial border of the scapula and supplies the rhomboid muscles and the levator scapulae. In dogs, the dorsal scapular artery is a consistent branch, and it is often visible during dissection of the scapular region. In cats, the dorsal scapular artery is smaller but follows a similar course.

How the Subclavian Artery Is Studied in Practice

The subclavian artery is studied through dissection, angiography, and cross-sectional imaging. Each method reveals different aspects of its anatomy.

Dissection

In the dissection laboratory, the subclavian artery is approached through the thoracic inlet. The brachiocephalic trunk is identified, and the subclavian arteries are traced laterally. The vertebral artery is found ascending through the transverse foramina of the cervical vertebrae. The internal thoracic artery is traced caudally behind the sternum. The thyrocervical and costocervical trunks are identified as short, wide branches that divide into their respective arteries.

Dissection is the gold standard for understanding the three-dimensional relationships of the subclavian artery, but it is time-consuming and requires careful preservation of small vessels. In dogs and cats, the subclavian artery is best approached from the left side, where the brachiocephalic trunk and the left subclavian artery are more accessible.

Angiography and Computed Tomography Angiography

Computed tomography angiography (CTA) is the preferred method for imaging the subclavian artery and its branches in living animals. CTA provides high-resolution images of the vessel lumen and wall, and it can detect anomalies such as aberrant right subclavian artery, vertebral artery origin variants, and subclavian artery stenosis.

A study of 75 CTA cases (150 vertebral arteries) found that the vertebral artery arose from the subclavian artery in 95.3% of cases, from the aortic arch in 2.7%, and the parent vessel was not recorded in 2.0% [2]. The most frequent origin levels were the T1 middle third (23.3%), T1 upper third (18.0%), T1 lower third (17.3%), and C7-T1 disc level (13.3%) [2]. Entry into the transverse foramen occurred at C6 in 90.7% of arteries, C5 in 6.0%, and C7 in 3.3% [2]. These data provide a baseline for interpreting vertebral artery anatomy in humans and a framework for understanding similar patterns in dogs and cats.

In veterinary medicine, CTA is used to evaluate the subclavian artery in cases of suspected vascular ring anomaly, thromboembolism, or trauma. The same principles apply: the vessel is traced from its origin to its continuation as the axillary artery, and its branches are identified and assessed for patency.

Doppler Ultrasound

Doppler ultrasound is a non-invasive method for assessing blood flow in the subclavian artery and its branches. It is particularly useful for evaluating the vertebral artery, where changes in flow velocity can indicate stenosis or occlusion. In humans, Doppler ultrasound is used to diagnose subclavian steal syndrome, a condition in which stenosis of the subclavian artery proximal to the vertebral artery origin causes retrograde flow in the vertebral artery. In veterinary medicine, Doppler ultrasound is used less frequently but can be helpful in assessing forelimb perfusion and detecting thromboembolism.

Embryology and Why Variants Occur

The subclavian artery develops from the fourth aortic arch and the seventh intersegmental artery. The right subclavian artery forms from the right fourth aortic arch and the right seventh intersegmental artery, while the left subclavian artery forms from the left seventh intersegmental artery. The vertebral artery develops from longitudinal anastomoses of the cervical intersegmental arteries [1].

Variants in the origin and course of the subclavian artery and vertebral artery arise from errors in this embryological process. An aberrant right subclavian artery, for example, occurs when the right fourth aortic arch involutes and the right subclavian artery arises from the descending aorta, passing behind the esophagus. This variant is well documented in humans and is associated with an increased risk of chromosomal abnormalities in fetuses [6].

In a postmortem case report, a five-vessel aortic arch was identified with a right common carotid artery, left common carotid artery, left vertebral artery arising directly from the arch, left subclavian artery, and an aberrant right subclavian artery with a retroesophageal course [7]. The right vertebral artery originated anomalously from the proximal right common carotid artery [7]. This rare configuration highlights the embryological complexity of multi-branch aortic arch variants and the importance of recognizing them before surgical or endovascular procedures [7].

In another case, a right vertebral artery arising from the right common carotid artery was associated with an aberrant right subclavian artery and a de novo V1 segment aneurysm [8]. A retrospective review of over 500 patients with an aberrant right subclavian artery found that the right vertebral artery arose from the right subclavian artery in 84% of patients and from the right common carotid artery in 16% of patients [9]. These data show that vertebral artery origin variants are not rare in the setting of an aberrant right subclavian artery, and they underscore the importance of preoperative imaging.

Clinical Relevance, Limitations and Common Mistakes

The subclavian artery is clinically relevant because it supplies the forelimb, the thoracic wall, and part of the brain. Stenosis or occlusion of the subclavian artery can cause forelimb claudication, thoracic wall ischemia, or vertebrobasilar insufficiency. In humans, subclavian artery stenosis is often asymptomatic because of well-developed collateral circulation, but it can cause coronary-subclavian steal syndrome in patients who have undergone coronary artery bypass grafting using the internal thoracic artery [4].

In veterinary medicine, subclavian artery pathology is less common but can occur in cases of thromboembolism, trauma, or vascular ring anomaly. The clinical signs depend on the location and severity of the lesion. Stenosis proximal to the vertebral artery origin can cause retrograde flow in the vertebral artery, leading to neurological signs. Stenosis distal to the vertebral artery origin can cause forelimb claudication.

The vertebro-subclavian artery angle is a morphological parameter that affects local blood flow patterns and the development of atherosclerosis at the vertebral artery origin. A study of 364 vertebral arteries found that a larger vertebro-subclavian artery angle was associated with an increased risk of plaque and stenosis (OR = 1.84, 95% CI: 1.46-2.33, P < 0.001), and severe curvature was also associated with increased risk (OR = 2.35, 95% CI: 1.21-4.56, P = 0.011) [10]. These findings suggest that the geometry of the vertebral artery origin is a determinant of local hemodynamics and atherosclerosis risk [10].

Common mistakes in learning the subclavian artery include:

• Assuming the human three-part model applies directly to dogs and cats. The scalene muscles and branching patterns differ, and the brachiocephalic trunk gives off both subclavian arteries in most domestic mammals.
• Forgetting that the vertebral artery can arise from the aortic arch or the common carotid artery in variant anatomy. In a study of 287 patients, aortic origin of the left vertebral artery was observed in 7.7% of patients [11].
• Confusing the thyrocervical trunk with the costocervical trunk. The thyrocervical trunk supplies the thyroid and scapular region, while the costocervical trunk supplies the deep neck and first two intercostal spaces.
• Overlooking the dorsal scapular artery. It is a small vessel but an important supplier of the rhomboid muscles and a potential collateral route in subclavian stenosis.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Review: Seven Points Worth Memorizing

1. The subclavian artery runs from its origin near the thoracic inlet to the outer border of the first rib, where it becomes the axillary artery.
2. In humans, the right subclavian artery arises from the brachiocephalic trunk and the left from the aortic arch.
3. In dogs and cats, the brachiocephalic trunk gives off both subclavian arteries.
4. The three parts of the subclavian artery are defined by their relationship to the anterior scalene muscle.
5. The first part gives off the vertebral artery, internal thoracic artery, and thyrocervical trunk.
6. The second part gives off the costocervical trunk, and the third part gives off the dorsal scapular artery.
7. Vertebral artery origin variants are common and clinically important, especially in the setting of an aberrant right subclavian artery.

Frequently Asked Questions

What is the subclavian artery?

The subclavian artery is the major artery that supplies the thoracic limb, ventral neck, and part of the brain. It runs from its origin near the thoracic inlet to the outer border of the first rib, where it becomes the axillary artery.

What are the three parts of the subclavian artery?

The three parts are defined by their relationship to the anterior scalene muscle: the first part is medial to the muscle, the second part is behind it, and the third part is lateral to it. Each part gives off specific branches.

What does the subclavian artery supply?

The subclavian artery supplies the forelimb, the ventral neck, the thoracic wall, and part of the brain through its branches. The vertebral artery supplies the brainstem and cerebellum, the internal thoracic artery supplies the thoracic wall and mammary glands, and the thyrocervical and costocervical trunks supply the neck and scapular region.

How does the subclavian artery differ in dogs and cats?

In dogs and cats, the brachiocephalic trunk gives off both subclavian arteries, unlike the human pattern where the left subclavian artery arises directly from the aortic arch. The thyrocervical and costocervical trunks also vary by species, and their branches may arise independently from the subclavian artery.

What is the vertebral artery?

The vertebral artery is a branch of the subclavian artery that ascends through the transverse foramina of the cervical vertebrae and enters the skull to supply the brainstem, cerebellum, and posterior cerebral circulation. It usually arises from the first part of the subclavian artery, but variant origins are well documented.

Why is the subclavian artery clinically important?

The subclavian artery is clinically important because stenosis or occlusion can cause forelimb claudication, thoracic wall ischemia, or vertebrobasilar insufficiency. In humans, subclavian stenosis can cause coronary-subclavian steal syndrome in patients who have undergone coronary artery bypass grafting using the internal thoracic artery.

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Sources

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4. Angioplasty Using Kissing Balloon Technique for Left Subclavian Artery Stenosis Concomitant with Origin of Vertebral Artery Stenosis Following Coronary Artery Bypass Using Internal Thoracic Artery: A Case Report.
5. Unilateral absence of the thyrocervical trunk with multiple subclavian arterial variations and a suprascapular artery traversing the brachial plexus: a cadaveric case report.
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