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CHAPTER VIII. 
Plate VII. — vertebr* of the human neck. 
Fig. 1. A representation of the head and the neck ; the latter is 
composed of seven bones called vertebra. 
Fig. 2. Exhibits the first and second vertebrae, with their mode 
of connexion. The uppermost vertebra, 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 sur¬ 
faces, 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, 6, 6, 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 correspond¬ 
ing indentation of the atlas, Fig. 3, 6, 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 lat¬ 
eral 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. 
