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Plate 7: Vertebrae of the Human Neck

Fig. 1. A representation of the head and the neck; the latter is composed of seven bones called vertebrae.

Fig. 2. Exhibits the first and second vertebrae, with their mode of connexion. The uppermost vertebrae, termed the atlas, from its supporting the globe of the head, has an oval concave surface on either side, a, a, for the reception of two corresponding convex surfaces placed on the lower part of the head, in such a manner as only to admit of the action of bending and raising the head.

Fig. 3. The atlas.

Fig. 4. The second vertebra, called dentata, has two plane surfaces, a, a, adapted to the planes, a, a, Fig. 3, of the atlas: and this manner of articulation provides for the turning of the head laterally in almost every direction. Fig. 2. and 4, b, b, show the tooth-like process which affords a firm pivot for the production of the lateral motion just described. This process is received into a corresponding indentation of the atlas, Fig. 3, b, and a strong ligament passes behind it, serving as an effectual security against dislocation, and consequent compression of the spinal marrow. Fig. 4, d, marks the situation for the spinal marrow, which passes through the ring of each vertebra. The letter, c, indicates a perforation in the lateral process; and, as there is a corresponding perforation in each lateral, or as it is termed, transverse process of the seven cervical vertebrae, a continuous passage is thus formed for the protection of two important blood-vessels destined to supply the brain.