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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
with the superior facets of the subjacent vertebræ, and on this account a considerable amount of lateral flexion is permitted. For the same reason a slight amount of rotation can be carried out, but this is so soon checked by the interlocking of the articular surfaces that it is negligible.
  The principal muscles which produce flexion are the Sternocleidomastoideus, Longus capitis, and Longus colli; the Scaleni; the abdominal muscles and the Psoas major. Extension is produced by the intrinsic muscles of the back, assisted in the neck by the Splenius, Semispinales dorsi and cervicis, and the Multifidus. Lateral motion is produced by the intrinsic muscles of the back by the Splenius, the Scaleni, the Quadratus lumborum, and the Psoas major, the muscles of one side only acting; and rotation by the action of the following muscles of one side only, viz., the Sternocleidomastoideus, the Longus capitis, the Scaleni, the Multifidus, the Semispinalis capitis, and the abdominal muscles.
 
5b. Articulation of the Atlas with the Epistropheus or Axis
 
  
(Articulatio Atlantoepistrophica)


The articulation of the atlas with the axis is of a complicated nature, comprising no fewer than four distinct joints. There is a pivot articulation between the odontoid process of the axis and the ring formed by the anterior arch and the tranverse ligament of the atlas (see Fig. 306); here there are two joints: one between the posterior surface of the anterior arch of the atlas and the front of the odontoid process; the other between the anterior surface of the ligament and the back of the process. Between the articular processes of the two bones there is on either side an arthrodial or gliding joint. The ligaments connecting these bones are:
Two Articular Capsules.
The Posterior Atlantoaxial.
The Anterior Atlantoaxial.
The Transverse.


FIG. 304– Anterior atlantoöccipital membrane and atlantoaxial ligament. (See enlarged image)


The Articular Capsules (capsulæ articulares; capsular ligaments).—The articular capsules are thin and loose, and connect the margins of the lateral masses of the atlas with those of the posterior articular surfaces of the axis. Each is strengthened at its posterior and medial part by an accessory ligament, which is attached

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