ee eel 
ARTICULATION OF ATLAS WITH AXIS. 257 
Thus lateral flexion is permitted in the lumbar, but not in the cervical or dorsal regions. 
Again, in the lumbar region rotation does not occur, owing to the shape of the articular processes, 
while it is possible in the dorsal region. In the cervical region the shape and position of the 
articular surfaces prevent the occurrence both of lateral flexion and of rotation as isolated move- 
ments, but a combination of these two movements may take place, whereby rotatory movement 
in an oblique median axis results. Finally, in the lumbar region, by combining the four forms 
of flexion, viz. forward, backward, and lateral, a certain amount of circumduction is possible. 
ARTICULATION OF ATLAS WITH AXIS. 
Between these two vertebree three diarthroses occur. Two of them are 
situated laterally in relation to the articular processes, and are called arthrodial 
diarthroses, because of the flattened nature of the articulating surfaces. The third 
articulation is mesial in position. It is found between the smooth anterior surface 
of the odontoid process of the axis and the articular facet on the posterior aspect of 
the anterior arch of the atlas. This joint is a rotatory diarthrosis. 
Ligaments.—Each of the joints is furnished with a capsular ligament whereby 
the joint cavity is circumscribed. In the case of the lateral articulations, each 
capsular ligament presents a distinct band, named the accessory ligament, which 1s 
i 
Go 
‘ 3 
i 
yMembrana tectoria 
: 4s SS 
Basi-oecipital bone— 
_-Superior crus of crucial ligament 
Synovial cavity P 
Posterior occipito-atloid 
ligament 
Anterior occipito-atloid ligament 
Ligamentum apicis dentis 
Synovial cavity 
Odontoid process 
Anterior arch of atlas — 
Transverse ligament of atlas 
Fic. 202.—MestaL SECTION THROUGH THE OCCIPITO-ATLOID AND ATLO-AXOID JOINTS. 
situated within the neural canal (Fig. 203), and passes downwards and inwards 
from the lateral mass of the atlas to the superior aspect of the body of the axis. 
The following additional ligaments constitute the leading bonds of union :— 
The anterior atlo-axoid ligament (Fig. 202) is a membranous structure which is 
thin laterally, but strong mesially where it is thickened by a prolongation of the 
anterior common ligament. It extends from the anterior arch of the atlas to the 
front of the body of the axis. 
The posterior atlo-axoid ligament (Fig. 202) occupies the position which is 
elsewhere taken by the ligamenta subflava. It extends from the posterior arch 
of the atlas to the upper border of the neural arch of the axis. 
The transverse ligament of the atlas (lig. transversum atlantis, Figs. 202 and 
203) is a strong band, placed transversely, which arches backwards behind the 
neck of the odontoid process of the axis. By its extremities it is attached to the 
tubercle on the inner aspect of each lateral mass of the atlas. A thin plate of 
fibro-cartilage is developed in its central part. 
Synovial membrane lines each of the three capsular ligaments, and in addition a 
synovial sac is developed between the odontoid process and the transverse ligament. © 
This is more extensive than the synovial cavity between the odontoid process and 
the atlas. 
