THE CERVICAL VERTEBRAE 



33 



ment divides the interior of the ring into a smaller anterior part for the dens of the axis, and a 

 larger posterior part, corresponding to the foramina of other vertebrae, for the spinal cord and 

 its membranes. 



The transverse processes are large and extend farther outward than those of the vertebra; 

 immediately below. They are flattened from above downward and each is perforated by a large 

 costo -transverse foramen; the extremity is not bifid, but, on the contrary, is broad and rough 

 for the attachment of numerous muscles. The posterior arch unites the lateral masses behind 

 and forms about two-fifths of the entire circumference. It presents in the middle line a rough 

 elevation or tubercle representing a rudimentary spinous process. At its junction with the 

 lateral mass on the superior surface is a deep groove, the sulcus arteriae vertebralis, which 



Fig. 36. — The First Cervical Vertebra or Atlas. 



Anterior tubercle 

 Superior articular process 



Costal process 



Costo-transverse foramen 



Transverse process 



Groove for vertebral artery 



Posterior tubercle 



lodges the vertebral artery and the sub-occipital (first spinal) nerve. The groove corresponds 

 to the superior notches of other vertebrae and occasionally it is converted into a foramen by a 

 bony arch — the ossified oblique ligament of the atlas. A similar but much shallower notch is 

 present on the inferior surface of the posterior arch, and, with a corresponding notch on the 

 axis, forms an intervertebral foramen for the exit of the second spinal nerve. The upper and 

 lower surfaces of the arch afford attachment to ligaments uniting the atlas to the occipital 

 bone and the axis. 



The atlas gives attachment to the following muscles: — 



Anterior arch Longus colli. 



Posterior arch Rectus capitis posterior minor. 



Transverse ;process Rectus capitis anterior (minor), rectus";capitis lateralis, 



obliquus capitis inferior, obliquus capitis superior, 

 splenius cervicis, levator scapulae, and intertransver- 

 sarii, anterior and posterior. 



Fig. 37. — The Epistropheus or Axis, 



Odontoid process (dens) 



Groove for transverse ligament ■ 

 Lamina 



Facet for atlas 



Superior articular process 



Costo-transverse foramen 



Body 



Costal process 



Spinous process Inferior articular process 



The Epistropheus (Axis) 



The epistropheus (axis) (fig. 37) is the thickest and strongest of the bones of 

 this region, and is so named from forming a pivot on which the atlas rotates, 

 carrying the head. It is easily recognised by the rounded dens (odontoid process) 

 which surmounts the upper surface of the body. This process, which represents 

 the displaced body of the atlas, is large, blunt, and tooth-like, and bears on its 

 anterior surface an oval facet for articulation with the anterior arch of the atlas; 

 posteriorly it presents a smooth groove which receives the transverse ligament. 

 To the apex a thin narrow fibrous band (the apical dental ligament) is attached, 

 and on each side of the apex is a rough surface for the attachment of the alar 



