292 



SYNDESMOLOGY 



I 



sition with the superior facets of the subjacent vertebrae, 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. 



II. Articulation of the Atlas with the Epistropheus or Axis (Articulatio 



Atlantoepistrophica ) . 



The articulation of the atlas with the axis is of a complicated nature, com- 

 prising 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 Anterior Atlantoaxial. 



The Posterior Atlantoaxial. 

 The Transverse. 



Atlanto- 



occipital ( Articular capsule 



embrane 



C Articular e< 

 and 

 {synovial me\ 



Articular capsule 



and 

 synovial membrane 



FIG. 304. Anterior atlantooccipital membrane and atlantoaxial ligament. 



The Articular Capsules (capsulae 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 strength- 

 ened at its posterior and medial part by an accessory ligament, which is attached 



