258 - THE ARTICULATIONS OR JOINTS. 
ARTICULATION OF SPINE WITH CRANIUM. 
There are two articulations between the atlas and the occiput. ach is a 
diarthrosis in which movement takes place in relation to two axes, viz. the 
transverse and the antero-posterior. The condyle of the occiput being biconvex, 
fits into the biconcave superior articular surface of the atlas, while the long axes of 
the two joints are directed horizontally forwards and inwards. 
Ligaments.—Each articulation is provided with a capsular ligament which is 
thin but complete. It is attached to the rough non-articular surfaces surrounding 
the articular areas on the atlas and occiput. 
The following supplementary ligaments are the chief structures which bind the 
atlas to the occiput :— 
The anterior occipito-atloid ligament (membrana atlanto-occipitalis anterior, 
Fig. 202) is a strong although thin membrane, attached inferiorly to the anterior 
arch of the atlas, and superiorly to the anterior half of the circumference of the 
foramen magnum. Laterally it is in continuity with the capsular ligaments, while 
in the mesial plane, where it extends from the anterior tubercle of the atlas to the 
basi-occiput, it presents a specially well-defined thickened band which might be 
regarded as a separate accessory ligament or as the beginning of the anterior 
common ligament of the vertebre. 
The posterior occipito-atloid ligament (membrana atlanto-occipitalis posterior, 
Fig. 202) is another distinct but still thin membrane which is attached superiorly 
to the posterior half of the circumference of the foramen magnum, and inferiorly to 
the upper border of the posterior arch of the atlas. Laterally it also is continuous 
with the capsular ligaments. On each side of the mesial plane its inferior border — 
is arched in relation to the vertebral groove, and is therefore to some extent free, — 
in order to permit the passage of the posterior primary division of the first cervical 
nerve and the vertebral artery. Not infrequently this arched border becomes 
ossified, thus converting the groove in the bone into a foramen. 
Synovial membrane lines each of the capsular ligaments. There is no direct 
articulation between the axis and the occiput, but union between them is effected 
by means of the following accessory ligaments. 
The posterior occipito- caxoid Pecans (membrana tectoria, Fig. 203) is situated 
within the neural canal, and is usually regarded as the upward continuation of the 
posterior common ligament of the vertebral bodies. It extends from the posterior 
-Membrana tectoria 
Crus superius 
Ligamentum apicis dentis 
(middle odontoid) 
Ligamentum alare 
or check ligament 
= _—--—Crus superius 
Ligamentum crucia- 
tum atlantis 
Accessory atlanto- 
axial ligament 
Crus inferius 
Membrana tectoria 
Fic. 203.—DIssECTION FROM BEHIND OF THE LIGAMENTS CONNECTING THE OCCIPITAL BONE, THE ATLAS, 
AND THE AXIS WITH EACH OTHER. 
surface of the body of the axis to the basilar groove on the upper surface of the | 
basi-occipital bone, spreading laterally on the circumference of the foramen 
magnum. Some of its deepest fibres are attached to the atlas immediately above 
the atlo-axoid articulation. 
