8 THE sk'i:Li:rox 



pretitnits a tubercle on its anterior fate for the anterior vertel)ral liframent and the 

 longas colli nui.-icle ; its posterior surface has a circuhir facet for the odontf^id process 

 of the axis. The upper and lower Iwrders are for ligaments. 



The lateral masses are united posteriorly by a larger arch of Iwne, forming two- 

 tiftlis of the c-ircumference. Posteriorly this arch has a tubercle, representing a 

 rudimentary si)inous process. The upper and under surfaces of the arch afford 

 attachments to ligaments. At the junction of the posterior arch Avith the lateral 

 masses there is, on the upper surface, a deep groove which lodges the vertebral 

 arti'rv and the suboccipital (first spinal) nerve. A bridge of bone (the ossified 



Fig. 8.— The First Cervical Vertebra or Atlas. 



ANTERIOR TUBERCLE 



SUPERIOR ARTICULAR PROCESS 



COSTAL PROCESS 



COSTO-TRANSVERSE FORAMEN 



TRANSVERSE PROCESS 



GROOVE FOR VERTEBRAL 

 ARTERY 



POSTERIOR TUBERCLE 



oblique ligament) sometimes converts this into a foramen. A similar, but nuich 

 shallower, notch is present on the under surface; this, with the axis, forms an 

 intervertebral foramen for the second nerve. The atlas and axis are peculiar in that 

 the first and second spinal nerves issue behind the articular processes, whereas the 

 remaining spinal nerves emerge in front of the articular facets of the vertebrae. 

 Each lateral mass has, on its upper surface, an elongated, deeply concave articular 

 fossa or cup. These articular cups convierge anteriorly. Occasionally each presents 

 two oval facets united by an isthmus. These cups receive the occipital condyles and 

 permit nodding movements of the head. The inferior articular processes are 



Fig. 9.— The Axis. 



odontoid process • 



"^ """ ' ^ facet for atlas 



GROOVE FOR TRANSVERSE LIGAMENT 

 LAMINA 



SUPERIOR ARTICULAR PROCESS 



COSTO-TRANSVERSE FORAMEN 

 BODY 



COSTAL PROCESS 



INFERIOR ARTICULAR PROCESS 



( ircular and almost flat; they are directed downwards, with an inclination inwards, 

 rest u})r)n the axis, and permit rotatory movements of the liead. I>et\veen the 

 upjx'r and lower articular surfaces on the inside of the ring, two tubercles exist for 

 the transverse ligament. This ligament divides the space within the ring into an 

 anterior smaller segment for the odontoid })rocess of the axis, and a larger ])ortion 

 — tlie spinal foramen of other vertebr£e — for the si)inal cord and its memljranes. 



The transverse processes are large, to serve for the attachment of muscles which 

 helj) to rotate tlie licail. The costo-transverse foramina are large, but the costal 

 processes are slender. 



