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. The axis defining feature is its strong odontoid process (bony protrusion) known as the dens, which rises dorsally from the rest of the bone. Structure
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. It presents a median longitudinal ridge in front, separating two lateral depressions for the attachment of the longus colli muscles. Dens
The dens, also called the odontoid process or the peg, is the most pronounced projecting feature of the axis. The dens exhibits a slight constriction where it joins the main body of the vertebra. 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. On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas. 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. The apex is pointed and gives attachment to the apical odontoid ligament. 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.
Haloperidol decanoate, sold under the brand name Haldol Decanoate among others, is a typical antipsychotic which is used in the treatment of schizophrenia. It is administered by injection into muscle at a dose of 100 to 200 mg once every 4 weeks or monthly. The dorsogluteal site is recommended. A 3.75-cm (1.5-inch), 21-gauge needle is generally used, but obese individuals may require a 6.5-cm (2.5-inch) needle to ensure that the drug is indeed injected intramuscularly and not subcutaneously. Haloperidol decanoate is provided in the form of 50 or 100 mg/mL oil solution of sesame oil and benzyl alcohol in ampoules or pre-filled syringes. Its elimination half-life after multiple doses is 21 days. The medication is marketed in many countries throughout the world. See also
List of antipsychotics § Antipsychotic esters


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