52 SPECIAL ANATOMY OF THE SKELETON 



segment receiving the odontoid process of the axis, the posterior allowing the 

 transmission of the spinal cord and its membranes. This part of the vertebral 

 canal is of considerable size, to afford space for the spinal cord; and hence lateral 

 displacement of the atlas may occur without compression of this structure. The 

 transverse processes are of large size, project directly outward and downward 

 from the lateral masses, and serve for the attachment of special muscles which 

 assist in rotating the head. They are long, not bifid, and perforated at their 

 bases by a canal for the vertebral artery, which is directed from below, upward, 

 and backward. 



Axis. The axis (epistropheus) (Fig. 17) is the pivot upon which the first 

 vertebra, carrying the head, rotates. The most distinctive character of this bone 

 is the strong, prominent process, tooth-like in form, which rises perpendicularly 

 from the upper surface of the body. The body is deeper in front than behind, 

 and prolonged downward anteriorly so as to overlap the upper and fore part of 

 the next vertebra. It presents in front a median longitudinal ridge, separating 

 two lateral depressions, for the attachment of the Longus colli muscles of either 

 side. The odontoid process presents two articulating surfaces covered with 

 cartilage; one in front, of an oval form, for articulation with the atlas (fades 

 articularis anterior}] another behind (fades articularis posterior), for the transverse 



Odontoidjprocess. 



Rough surface for check ligaments. 



.Articular surface for 



___ atlas. 



Articular surface for transverse ligament. - 



-Body. 



mr ^HNFW *^' /% .n 



Spinous process.-* 



w*jfff -mt^ _ 



i Trmuvene process. 

 Inferior articular process. 

 FIG. 17. Second cervical vertebra, or axis. 



ligament the latter frequently encroaching on the sides of the process. The 

 apex is pointed, and gives attachment to the middle odontoid ligament. Below 

 the apex the process is somewhat enlarged, and presents on either side a rough 

 impression for the attachment of the lateral fasciculi of the odontoid or check 

 ligaments, which connect it to the occipital bone; the base of the process, where 

 it is attached to the body, is constricted, so as to prevent displacement from the 

 transverse ligament, which binds it in this situation to the anterior arch of the 

 atlas. The pedicles are broad and strong, especially their anterior extremities, 

 which coalesce with the sides of the body and the root of the odontoid process. 

 The laminae are thick and strong, and the spinal foramen large, but smaller 

 than that of the atlas. The transverse processes are very small, not bifid, and each 

 is perforated by the foramen for the vertebral artery, which is directed obliquely 

 upward and outward. The superior articular surfaces (fades articulares superiores) 

 are circular, slightly convex, directed upward and outward, and are peculiar 

 in being supported on the body, pedicles, and transverse processes. The inferior 

 articular surfaces (fades articulares inferiores) have the same direction as those 

 of the other cervical vertebra;. The superior intervertebral notches are very 

 shallow, and lie behind the articular processes; the inferior in front of them, 



