THE HEAD AND NECK 1305 



The vertical portion ol the cruciform ligament consists of two 

 parts, upper and lower, which are spoken of as the superior cms 

 and inferior cms. The superior crus extends from the posterior 

 surface of the transverse ligament at the median line to the pos- 

 terior part of the basilar groove of the occipital bone, between the 

 anterior margin of the foramen magnum and the superior attach- 

 ment of the membrana tectoria, under cover of which latter it lies. 

 This cms, as it ascends, is in contact with the posterior surface of 

 the head of the odontoid process. The inferior crus extends from 

 the posterior surface of the transverse ligament at the median line 

 to the posterior surface of the body of the axis above the inferior 

 attachment of the membrana tectoria. 



The transverse portion of the cruciform ligament constitutes the 

 transverse ligament of the atlas, already described. 



The middle odontoid or suspensory ligament is a narrow round 

 cord which is attached inferiorly to the ridge on the head of the 

 odontoid process, and superiorly to the anterior margin of the 

 foramen magnum in the median line. 



The lateral odontoid or alar ligaments, also known as the check 

 ligaments, form two very strong bands which are attached in- 

 feriorly to the lateral surfaces on the head of the odontoid process, 

 and superiorly to an impression on the inner surface of each con- 

 dylar part of the occipital bone. The direction of each Hgament 

 is outwards and shghtly upwards. 



Movements — Atlanto-Axial Joints. — The movements are of a rotatory kind, 

 the atlas, bearing the head, rotating on the axis, the odontoid process of which 

 serves as a pivot. The extent of rotation is about 30 degrees, and it is Umited 

 by the lateral odontoid Ugaments. aided shghtly by the accessory- atlanto-axial 

 Ugaments. As stated in the section on Osteology, the superior articular pro- 

 cesses of the axis are each divided by a sUght transverse elevation into t\vo 

 parts — anterior and posterior. When the atlas hes directly over the axis, as 

 when the face is directed straight forwards, the inferior articular processes of 

 the atlas are not in accurate contact with the superior articular processes of 

 the axis. Between the contiguous pairs there is a distinct interval all round. 

 When, however, the atlas is rotated, the anterior division of the axial articular 

 process of one side is brought into accurate contact with the corresponding 

 atlantal articular process, and the posterior division of the opposite axial 

 articuleir process into accurate contact with the atlantal articular process of 

 that side. AUanto-oeeipital Joints. — The movements allowed at these joints 

 are as follows: (i) Flexion; (2) extension; and (3) oblique movement. Flexion 

 and extension constitute the forward and backward, or nodding, movements. 

 In overextension (dorsi-flexion) the posterior margins of tiie superior articular 

 processes of the atlas enter the posterior condylar fosses of the occipital bone, 

 and locking takes place. In complete fonvard or ventral flexion the anterior 

 margins of the superior articular processes of the atlas come into contact with 

 the occipital bone in front of each condyle. 



Oblique movement occurs in the position of semiflexion ventralwards. As 

 stated in the section on Osteology, the condyles of the occipital bone, like 

 the superior articular processes of the axis, are each divided into two parts, 

 anterior and posterior, by a sUght elevation, which, in the case of the occipital 

 condyles, is disposed obUquely. During obhque movement the anterior 

 division of one occipital condyle is in contact with the corresponding superior 

 articular process of the atlas, whilst the posterior division of the opposite occi- 

 pital condyle is in contact with the superior articular process of the atlas on 

 that side. 



