# Cervical Spine Anatomy: Vertebrae Explained for Students The mammalian cervical spine almost always contains exactly seven vertebrae, labeled C1 through C7 from skull to thorax, and this number is remarkably conserved across species from the mouse to the giraffe. What changes between species is not the count but the shape, the size, and the orientation of the individual bones, and those differences explain why a dog can scratch its ear with a hind foot while a horse cannot, and why a human can turn the head through a wide arc while a dog's neck is built for forward reach and low-amplitude rotation. This guide walks through the cervical vertebrae one at a time, using the dog and horse as the primary veterinary models and the human as a familiar comparison. It covers the atlas (C1), which has no vertebral body, the axis (C2), which carries the dens, and the bifid spinous processes of C3 to C6 that appear in many domestic mammals. It also covers the clinical landmarks that matter in practice: the atlanto-occipital joint, the transverse foramina that transmit the vertebral artery, and the C7 vertebra prominens. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Why Seven Cervical Vertebrae? The near-universal count of seven cervical vertebrae in mammals is one of the most striking examples of evolutionary conservation in the vertebrate skeleton. Giraffes have seven cervical vertebrae, the same number as humans and dogs, but each giraffe vertebra can exceed 25 cm in length. Elephants also have seven, and a computed tomography study of the Asian elephant cervical spine documented the morphometric variation in vertebral body height, spinous process height, transverse process width, and vertebral foramen volume across the series [1]. Two features of the cervical region make it distinct from the rest of the vertebral column. First, the cervical vertebrae are the only vertebrae that consistently possess transverse foramina, openings in the transverse processes that transmit the vertebral artery and its accompanying venous plexus. Second, the cervical vertebrae are the most mobile segment of the vertebral column in most species, a direct consequence of their relatively small vertebral bodies, their overlapping articular processes, and the absence of the heavy rib attachments that stiffen the thoracic spine. The functional demands on the neck differ enormously between species. A horse uses the neck as a counterbalance during galloping and as a lever for grazing and rearing. A dog uses the neck for olfaction, prey capture, and social signaling. A human uses the neck primarily to stabilize a large head above a vertical trunk and to orient the sensory organs. These different demands produce different bone shapes even though the segmental plan is identical. ## The Atlas (C1): The Vertebra Without a Body The first cervical vertebra is called the atlas, named after the mythological figure who held up the sky. The atlas is unique among vertebrae because it lacks a vertebral body. Instead, it forms a ring composed of a dorsal arch, a ventral arch, and two lateral masses. The ring encircles the spinal cord and the dens of the axis, and the lateral masses bear the articular surfaces that connect to the skull above and the axis below. The atlanto-occipital joint is the articulation between the occipital condyles of the skull and the cranial articular foveae of the atlas. This joint permits the nodding motion of the head, which anatomists call flexion and extension. In the dog, the atlas has broad, wing-like transverse processes that project laterally and can be palpated just caudal to the skull. In the horse, the atlas is similarly broad but more massive, reflecting the greater load imposed by the equine head. A study of the Asian elephant atlas found two dorsal tubercles with a groove between them on the dorsal arch, a feature not present in the horse or ox [1]. This kind of species-specific detail is exactly what a comparative anatomy course is designed to teach. The atlas is not a generic ring. It is a ring shaped by the muscles and ligaments that attach to it and by the range of motion the species requires. The dog has a specialized ligamentous structure at the C1 to C2 level that supports the spinal cord within the vertebral canal, a pair of ligaments that appear to be an adaptation to the extreme mobility of the cranial cervical region [2]. This is a reminder that cervical anatomy is not just bone. The soft tissues that stabilize the bones are equally important, and in the dog they are distinct enough to have been described as a new anatomical structure. ## The Axis (C2): The Vertebra With the Dens The second cervical vertebra is called the axis because it forms the pivot around which the atlas and skull rotate. Its defining feature is the dens, also called the odontoid process, a bony peg that projects cranially from the vertebral body and lies within the ring of the atlas. The dens is the embryological remnant of the body of the atlas, which fuses with the axis during development. The atlantoaxial joint is the articulation between the atlas and the axis. It permits rotation of the head, which is why you can turn your head from side to side. In the dog, the atlantoaxial joint is relatively shallow and relies heavily on the transverse ligament of the atlas and the alar ligaments to hold the dens in place. Failure of these ligaments, or malformation of the dens, can cause atlantoaxial instability, a condition seen most often in small breed dogs such as Yorkshire Terriers and Chihuahuas. The orientation of the odontoid process varies between species. A comparative ontogenetic study of human and ape cervical vertebrae found that the orientation of the odontoid process in adult humans and adult chimpanzees is similar, but the developmental pathways that produce it are distinct, with humans achieving the adult morphology much earlier [3]. This tells us that the dens is not just a static landmark. Its shape and orientation are the product of developmental timing, and those differences can have biomechanical consequences. In the horse, the axis is a large, robust bone with a prominent dens and a heavy spinous process that projects caudally. The equine axis is one of the strongest bones in the cervical spine, reflecting the forces generated by the nuchal ligament and the muscles that suspend the head. ## C3 to C6: The Subaxial Vertebrae and Bifid Spinous Processes The third through sixth cervical vertebrae are the subaxial vertebrae. They share a common plan: a vertebral body, a vertebral arch, a spinous process, transverse processes with transverse foramina, and cranial and caudal articular processes. In many domestic mammals, including the dog and the cat, the spinous processes of C3 through C6 are bifid, meaning they split into two tubercles at their dorsal end. The bifid spinous process is a useful landmark for students because it helps distinguish cervical vertebrae from thoracic vertebrae, which have single, longer spinous processes. In the dog, the bifid spinous processes are well developed and can be seen on radiographs. In the horse, the spinous processes of C3 to C6 are less distinctly bifid but still show a dorsal cleft in many specimens. A radiographic and anatomical study of cervical vertebrae in adult Persian cats found that C3 had the lowest spinous process height and C7 had the highest, and that the atlas had the highest transverse process width, significantly different from the other cervical vertebrae [4]. This kind of quantitative data is valuable because it gives students a baseline for what is normal in a specific species. The Persian cat is not a dog, and its cervical proportions differ in ways that matter for radiographic interpretation. The transverse processes of the subaxial vertebrae are also important. They carry the transverse foramina, which transmit the vertebral artery. The vertebral artery is a major source of blood to the brain, and its course through the cervical vertebrae is a key consideration in any surgical or traumatic injury to the neck. In the horse, the transverse processes of C6 and C7 have a distinctive ventral lamina, a ventral extension that is unique to these two vertebrae. A study of 100 horses found that morphologic variations of the C6 ventral lamina were present in 24 of them, with symmetric absence in nine and asymmetric absence in 15 [5]. Anomalous C6 vertebrae were more common in Warmbloods, with 19 of 55 Warmbloods affected [5]. A separate study of Warmblood horses found that congenital variants of the ventral laminae of C6 and C7 were not associated with clinical signs or other radiological abnormalities of the cervicothoracic region [6]. This is an important point for students: a variation seen on a radiograph is not automatically a disease. The clinical context determines whether a finding matters. ## C7: The Vertebra Prominens The seventh cervical vertebra is called the vertebra prominens because its spinous process is the most prominent of the cervical series. Unlike the bifid spinous processes of C3 to C6, the spinous process of C7 is typically a single, stout tubercle that is not bifid. This makes C7 a useful landmark for counting vertebrae on radiographs and for palpating the caudal cervical spine. In the horse, C7 is the last cervical vertebra and articulates with the first thoracic vertebra. The transition from C7 to T1 is a common site for congenital variants, including rudimentary first ribs and transitional vertebrae. A study of 78 horses found that one horse had rudimentary first ribs bilaterally and one had bilateral transverse processes at T1, representing homeotic changes [7]. These variants are not necessarily pathological, but they can complicate the interpretation of radiographs and the planning of surgical approaches. In the dog, C7 is a relatively short vertebra with a single spinous process. The C7 vertebra is a common site for cervical spondylomyelopathy, also known as wobbler syndrome, particularly in Doberman Pinschers and Great Danes. A study of 63 dogs with disc-associated cervical spondylomyelopathy found that the main site of spinal cord compression was commonly C6-7 or C5-6, and that 57% of dogs had multiple sites of compression [8]. This is why a thorough imaging workup is essential before any treatment decision. ## Comparative Table: C1 to C7 in Dog, Horse, and Human | Feature | Dog | Horse | Human | |--|--|--|--| | Total cervical vertebrae | 7 | 7 | 7 | | C1 body | Absent | Absent | Absent | | C1 transverse processes | Broad, wing-like | Broad, massive | Small, fused to lateral masses | | C2 dens | Present, short | Present, robust | Present, tall | | Bifid spinous processes | C3 to C6, well developed | C3 to C6, less distinct | Rare, usually single | | C7 spinous process | Single, prominent | Single, prominent | Single, prominent (vertebra prominens) | | Transverse foramina | Present in all cervical vertebrae | Present in all cervical vertebrae | Present in all cervical vertebrae | | Ventral lamina on C6 | Absent | Present, variable | Absent | | Neck length relative to body | Short to moderate | Long | Short | | Primary neck function | Reach, olfaction, balance | Counterbalance, grazing, rearing | Head stabilization, orientation | ## Clinical Landmarks for Students ### The Atlanto-Occipital Joint The atlanto-occipital joint is the articulation between the skull and the atlas. It is a condylar joint that permits flexion and extension, which is the nodding motion of the head. In the dog, this joint is relatively superficial and can be palpated just caudal to the skull. In the horse, the joint is deeper and is covered by heavy musculature. The joint is a common site for congenital malformations, including occipito-atlantal malformation, which was identified in one of 78 horses in a CT study [7]. ### The Transverse Foramina The transverse foramina are openings in the transverse processes of the cervical vertebrae that transmit the vertebral artery and vein. They are present in all seven cervical vertebrae in most mammals, although the size and shape vary. The vertebral artery enters the transverse foramen of C6 and ascends through the foramina of C5, C4, C3, C2, and C1 before entering the skull through the foramen magnum. This course is clinically important because trauma or surgical manipulation of the cervical vertebrae can compromise vertebral artery blood flow. ### The C7 Vertebra Prominens The C7 vertebra prominens is the most prominent spinous process in the cervical spine. It is a useful landmark for counting vertebrae on radiographs and for palpating the caudal cervical spine. In the horse, the C7 spinous process is large and can be palpated at the base of the neck. In the dog, it is smaller but still identifiable. ### The Cervical Articular Process Joints The articular process joints of the cervical vertebrae are the synovial joints between the cranial and caudal articular processes of adjacent vertebrae. These joints are innervated by the medial branch of the dorsal ramus of the cervical spinal nerves. A cadaveric study in horses found that each examined cervical articular process joint, except for C2 to C3, presented a dual nerve supply, with the joint receiving innervation from the nerve exiting at the same level and from the nerve exiting one level cranial [9]. This dual innervation is important for understanding why pain from cervical facet joints can be difficult to localize. ## Practical Implications for Owners and Keepers Cervical spine anatomy matters in everyday animal care. A dog with a neck injury may hold its head low and resist lifting. A horse with cervical vertebral stenotic myelopathy may show ataxia, which is a loss of coordination, and weakness. A cat with a cervical disc problem may cry out when picked up. Understanding the anatomy helps owners recognize when a problem is likely to be cervical rather than thoracic or lumbar. The cervical spine is the most mobile part of the vertebral column, so it is vulnerable to trauma from falls, vehicle accidents, and rough handling. It is also a common site for degenerative conditions, especially in large breed dogs and in horses. Owners should be aware that the neck is a delicate region. Rough pulling on a leash, especially with a choke chain, can injure the cervical spine. A harness that distributes force across the chest is generally safer than a collar for dogs with cervical disease. For horses, improper use of a twitch or a chain shank can cause sudden flexion of the neck and exacerbate cervical pain. ## Clinical Relevance, Limitations and Common Mistakes The clinical relevance of cervical vertebrae anatomy is broad. It informs the diagnosis of cervical spondylomyelopathy, atlantoaxial instability, cervical vertebral stenotic myelopathy, and cervical facet joint osteoarthritis. It guides the placement of ultrasound-guided injections, such as the inter-transversospinalis plane block in dogs, which targets the dorsal rami of the spinal nerves at C5 [10]. It also informs surgical planning for cervical spine reconstruction, although surgical techniques are outside the scope of this article. A common mistake is to assume that all cervical vertebrae look alike. They do not. The atlas has no body, the axis has a dens, and the subaxial vertebrae have bifid spinous processes in many species. Another mistake is to assume that a radiographic variant is always pathological. The C6 ventral lamina variant in horses is a good example: it is common, especially in Warmbloods, and is not associated with clinical signs in most cases [5][6]. A third mistake is to underestimate the importance of soft tissues. The cervical spine is stabilized by a complex array of ligaments, including the nuchal ligament, the dorsal atlantoaxial ligament, and the alar ligaments. In the dog, a newly described pair of ligaments supports the spinal cord at the C1 to C2 level [2]. Injury to these ligaments can cause instability even when the bones appear normal on radiographs. A fourth mistake is to rely on radiographs alone. Computed tomography and magnetic resonance imaging provide much more detail about the cervical spine. A study of 78 horses used CT to identify morphologic variations that would not have been visible on plain radiographs [7]. In dogs, MRI is the imaging modality of choice for cervical spondylomyelopathy because it shows the spinal cord, the intervertebral discs, and the ligaments [8]. Individual cases require a veterinarian for diagnosis and treatment. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Frequently Asked Questions ### How many cervical vertebrae do dogs have? Dogs have seven cervical vertebrae, labeled C1 through C7. This is the same number as in humans, horses, and almost all other mammals. ### What is the difference between the atlas and the axis? The atlas is C1 and has no vertebral body. The axis is C2 and has a dens, which is a bony peg that articulates with the atlas. The atlas permits nodding, and the axis permits rotation. ### Why do dogs have bifid spinous processes? Bifid spinous processes are split into two tubercles at the dorsal end. They are present on C3 to C6 in dogs and many other domestic mammals. They provide additional surface area for muscle attachment and help distinguish cervical vertebrae from thoracic vertebrae. ### Do horses have the same number of cervical vertebrae as dogs? Yes. Horses have seven cervical vertebrae, just like dogs and humans. The count is conserved across mammals, but the shape and size of the vertebrae differ between species. ### What is the vertebra prominens? The vertebra prominens is C7. Its spinous process is the most prominent of the cervical series, which makes it a useful landmark for counting vertebrae and for palpating the caudal cervical spine. ### What are the transverse foramina? The transverse foramina are openings in the transverse processes of the cervical vertebrae. They transmit the vertebral artery and vein, which supply blood to the brain. ### What is the atlanto-occipital joint? The atlanto-occipital joint is the articulation between the skull and the atlas. It permits flexion and extension of the head, which is the nodding motion. ### Can cervical spine problems be prevented? Some cervical spine problems are congenital and cannot be prevented. Others, such as those caused by trauma, can be reduced by using a harness instead of a collar for dogs and by handling horses gently. Early recognition of signs such as neck pain, stiffness, or ataxia can lead to earlier diagnosis and treatment. ## Related Articles - [Snake Anatomy: Do Snakes Have Teeth, Spines, and Other Structures?](/knowledge/veterinary-medicine/reptile-care/snake-anatomy-do-snakes-have-teeth-spines-and-other-structures) - [Guinea Pig Cervical Lymphadenitis: Diagnosis, Drainage, and Infection Control](/knowledge/veterinary-medicine/small-mammal-care/guinea-pig-cervical-lymphadenitis-diagnosis-drainage-infection-control) - [Imaging the Canine and Feline Spine: Radiography and Advanced Modalities](/knowledge/veterinary-medicine/diagnostic-imaging/imaging-canine-feline-spine-radiography-advanced-modalities) - [Surgical Approaches to the Spine: Dorsal and Ventral Exposure](/knowledge/veterinary-medicine/veterinary-surgery/surgical-approaches-spine-dorsal-ventral) - [Comparative Anatomy of the Mammalian Kidney](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/comparative-anatomy-mammalian-kidney) - [Comparative Anatomy of the Mammalian Heart](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/comparative-anatomy-mammalian-heart) - [Spinal Column Vertebrae: Regions and Structure](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/spinal-column-vertebrae-regions-and-structure) - [Vertebrae Lumbales: Lumbar Vertebrae Anatomy](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/vertebrae-lumbales-lumbar-vertebrae-anatomy) - [Vertebral Column: Vertebra Anatomy and Regions Explained](/blog/guides/vertebral-column-vertebra-anatomy-and-regions-explained) ## Sources 1. 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[Congenital variants of the ventral laminae of the sixth and seventh cervical vertebrae are not associated with clinical signs or other radiological abnormalities of the cervicothoracic region in Warmblood horses.](https://pubmed.ncbi.nlm.nih.gov/38938125/) 7. [EX VIVO COMPUTED TOMOGRAPHIC EVALUATION OF MORPHOLOGY VARIATIONS IN EQUINE CERVICAL VERTEBRAE.](https://pubmed.ncbi.nlm.nih.gov/27438135/) 8. [Magnetic resonance imaging and neurological findings in dogs with disc-associated cervical spondylomyelopathy: a case series.](https://pubmed.ncbi.nlm.nih.gov/33827551/) 9. [Anatomy and Ultrasound-Guided Injection of the Medial Branch of the Dorsal Ramus of the Cervical Spinal Nerves in the Horse: A Cadaveric Study.](https://pubmed.ncbi.nlm.nih.gov/32777844/) 10. [Cadaveric study of the ultrasound-guided inter-transversospinalis plane block in dogs for the cervical epaxial musculature region.](https://pubmed.ncbi.nlm.nih.gov/39369671/)