The uppermost cervical vertebra atlas (C1) articulates with the occipital bone superiorly and the second cervical vertebra, the axis, inferiorly. In addition, between adjacent vertebrae there is a passageway to allow spinal nerves to pass from the spinal cord to the body. The two vertebral arteries are especially important as at the base of the skull they merge to form the single basilar artery which supplies the brain stem and cerebellum with blood and then splits into the two posterior cerebral arteries that join with branches of the internal carotid artery to supply the cerebrum. All cervical vertebrae have a large central foramen known as the vertebral foramen to allow passage of the spinal cord and two laterally known as the transverse foramen to allow passage of the vertebral blood vessels. We will discuss the first two vertebra in detail but the next five are very similar in appearance and will be lumped together under the heading of typical cervical vertebra. Humans have seven cervical vertebrae which is also true of virtually all mammal species, except the manatee and two species of sloths, which only have 6. The cervical vertebrae act to support the skull, allow for movement of the head on the neck and some movement of the neck itself, in addition to protecting the spinal cord. In this case they are the greater and lesser horns of the hyoid. The cornu, like many structures, are also referred to by another name. The smaller more anterior one is known as the lesser cornu and the one at the posterior extent of the bone is the greater cornu. Anatomically the main central part of the hyoid is known as the body (above) and projecting superiorly are two superiorly placed projections.
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