ATLAS AND AXIS. 



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to its passage through the dura mater, and the first cervical nerve. 

 The intervertebral notches are peculiar from being situated behind 

 the articular processes instead of 

 before them, as in the other verte- 

 brae. The transverse processes are 

 remarkably large and long, and 

 pierced by the foramen for the 

 vertebral artery. The articular 

 processes are situated upon the 

 most bulky and strongest parts of 

 the atlas. The superior are oval 

 and concave, and look inwards, 

 so as to form a kind of cup for the condyles of the occipital bone* 

 and are adapted to the nodding movements of the head ; the inferior 

 are circular, and nearly horizontal, to permit of the rotary move- 

 ments. Upon the inner face of the lateral mass which supports the 

 articular processes, is a small tubercle at each side, into which the 

 extremities of the transverse ligament are attached, a ligament 

 which divides the ring of the atlas into two unequal segments ; the 

 smaller for receiving the odontoid process of the axis, and the latter 

 to give passage to the spinal cord and its membranes. 



The Jlxis is named from having a process upon which the head 

 turns as on a pivot. The body is of a large size, and supports a 

 strong process, the odontoid, which rises perpendicularly from 

 its upper surface. The odontoid process (processus dentatus) pre- 

 sents two articulating surfaces ; one on its anterior face, to articu- 

 late with the anterior arch of the atlas ; the other on its posterior 

 face, for the transverse ligament. Upon each side of its apex is a 

 rough depression, for the attachment of the 

 alar, or moderator ligaments. The lamince 

 are large and strong, and unite posteriorly to 

 form a long and projecting spinous process. 

 The transverse processes are quite rudimen- 

 tary, not bifid, and project only so far as to 

 enclose the vertebral foramen, which is di- 

 rected obliquely outwards instead of perpen- 

 dicularly as in the other vertebrae. The 

 superior articulating processes are situated 

 upon the body of the vertebra on each side of the odontoid process. 



* The upper surface of the atlas. 1. The anterior tubercle projecting from the 

 anterior arch. 2. The articular surface for the odontoid process upon the posterior sur- 

 face of the anterior arch. 3. The posterior arch, with its rudimentary spinous pro- 

 cess. 4. The intervertebral notch. 5. The transverse process. 6*. The vertebral fora- 

 men. 7. Superior articular surface. 8. The tubercle for the attachment of the 

 transverse ligament. 



t A lateral view of the axis. 1. The body. 2. The odontoid process. 3. The 

 smooth facet on the anterior surface of the odontoid process which articulates with the 

 anterior arch of the atlas. 4. The lamina. 5. The spinous process. 6. The trans- 

 verse process pierced obliquely by the vertebral foramen. 7. The superior articular 

 surface.- 8.. The inferior articular process.. 



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