颈椎 - Vertebrae cervicales [C I-C VII]
Cervical vertebræ are the smallest of the true vertebræ, and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen in each transverse process. The first, second, and seventh present exceptional features and must be separately described; the following characteristics are common to the remaining four :
- The body is small, and broader from side to side than from before backward.
- The anterior and posterior surfaces are flattened and of equal depth; the former is placed on a lower level than the latter, and its inferior border is prolonged downward, so as to overlap the upper and forepart of the vertebra below.
- The upper surface is concave transversely, and presents a projecting lip on either side;
- the lower surface is concave from before backward, convex from side to side, and presents laterally shallow concavities which receive the corresponding projecting lips of the subjacent vertebra.
- The pedicles are directed lateralward and backward, and are attached to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time, narrower.
- The laminæ are narrow, and thinner above than below;
- the vertebral foramen is large, and of a triangular form.
- The spinous process is short and bifid, the two divisions being often of unequal size.
- The superior and inferior articular processes on either side are fused to form an articular pillar, which projects lateralward from the junction of the pedicle and lamina. The articular facets are flat and of an oval form: the superior look backward, upward, and slightly medialward: the inferior forward, downward, and slightly lateralward.
- The transverse processes are each pierced by the foramen transversarium,which, in the upper six vertebræ, gives passage to the vertebral artery and vein and a plexus of sympathetic nerves. Each process consists of an anterior and a posterior part.
- The anterior portion is the homologue of the rib in the thoracic region, and is therefore named the costal process or costal element: it arises from the side of the body, is directed lateralward in front of the foramen, and ends in a tubercle, the anterior tubercle.
- The posterior part, the true transverse process, springs from the vertebral arch behind the foramen, and is directed forward and lateralward; it ends in a flattened vertical tubercle, the posterior tubercle. These two parts are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus on its upper surface for the passage of the corresponding spinal nerve.
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