The body and vertebral arch are ossified in the same manner as the corresponding parts in the other vertebrae, viz., one centre for the body, and two for the vertebral arch. The axis is ossified from five primary and two secondary centres. This is because a malformed odontoid process may lead to instability between the atlas and axis (the C1 and C2 cervical vertebrae).ĭevelopment The axis is ossified from five primary and two secondary centers. The spinous process is large, very strong, deeply channelled on its under surface, and presents a bifurcated extremity.Ĭontact sports are contraindicated for individuals with anomalous dens, as any violent impact may result in a catastrophic injury. The inferior vertebral notches lie in front of the articular processes, as in the other cervical vertebrae. The superior vertebral notches are very shallow, and lie behind the articular processes. The inferior articular surfaces have the same direction as those of the other cervical vertebrae. The superior articular surfaces are round, slightly convex, directed upward and laterally, and are supported on the body, pedicles, and transverse processes. Each process is perforated by the transverse foramen, which is directed obliquely upward and laterally. The transverse processes are very small, and each ends in a single tubercle. The vertebral foramen is large, but smaller than the atlas. They play a large role in the stability of the cervical spine alongside the laminae of C7. They are covered above by the superior articular surfaces. The pedicles are broad and strong, especially in the front, where they coalesce with the sides of the body and the root of the odontoid process. It is the fibrous remnant of the notochord. The weak apical ligament lies in front of the upper longitudinal bone of the cruciform ligament and joins the apex of the deltoid peg to the anterior margin of the foramen magnum. The inner ligaments limit rotation of the head and are very strong. The alar ligaments, together with the apical ligaments, are attached from the sloping upper edge of the odontoid peg to the margins of the foramen magnum. The peg has an articular facet at its front and forms part of a joint with the anterior arch of the atlas. The odontoid peg is the ascension of the atlas fused to the ascension of the axis. The internal structure of the odontoid process is more compact than that of the body. Below the apex, the process is somewhat enlarged and presents on either side a rough impression for the attachment of the alar ligament these ligaments connect the process to the occipital bone. The apex is pointed and gives attachment to the apical odontoid ligament. On the back of the neck, and frequently extending on to its lateral surfaces, is a shallow groove for the transverse atlantal ligament which retains the process in position. On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas. The condition where the dens is separated from the body of the axis is called os odontoideum and may cause nerve and circulation compression syndrome. The dens exhibits a slight constriction where it joins the main body of the vertebra. The dens, also called the odontoid process or the peg, is the most pronounced projecting feature of the axis. It presents a median longitudinal ridge in front, separating two lateral depressions for the attachment of the longus colli muscles.Īxis Odontoid Process of Axis (Dens) The body is deeper in front or in the back and is prolonged downward anteriorly to overlap the upper and front part of the third vertebra. The axis' defining feature is its strong odontoid process (bony protrusion) known as the dens, which rises dorsally from the rest of the bone. In anatomy, the axis (from Latin axis, "axle") or epistropheus is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests.
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