TEMPORO-MANDIBULAR JOINT. 259 
Subjacent to the preceding ligament there is the ligamentum cruciatum atlantis 
(Fig. 203), a structure which is very closely associated with the lig. transversum 
atlantis. It consists of a crus transversum, formed by the superficial fibres of 
the transverse ligament of the atlas; a crus inferius, consisting of mesial longi- 
tudinal fibres which are attached below to the posterior surface of the body of the 
axis, and above to the crus transversum and a crus superius, also mesial and 
longitudinal, whose fibres extend from the crus transversum upwards to the 
posterior surface of the basi-occiput, immediately subjacent to the posterior 
occipito-axoid ligament. 
The check ligaments or lateral odontoid ligaments (ligamenta alaria, Fig. 205) are 
two very powerful, short, and somewhat rounded bands. They are attached mesially 
to the sides of the summit of the odontoid process, and laterally to the tubercle 
_ on the inner aspect of the condylar portions of the occipital bone, viz. the ex- 
occipital bones. 
The middle odontoid ligament (ligamentum apicis dentis, Fig. 205) consists of 
fibres running vertically upwards from the apex of the odontoid process to the 
mesial part of the anterior margin of the foramen magnum. ‘This lgament 
_ to some extent represents an intervertebral disc, in the centre of which, remains of 
the notochord may be regarded as present. 
Even in advanced life a small lenticular mass of cartilage, completely sur- 
rounded by bone, persists in the plane of fusion between the odontoid process and 
' the body of the axis. 
Movements at these Joints.—At the joints between occiput and atlas the movements are 
_ very simple, and consist essentially of movements whereby the head is elevated and depressed 
upon the vertebral column (nodding movements). In addition a certain amount of oblique 
~ movement is possible, during which great stability is attained by resting the front and hinder 
_ parts of opposite condyles upon corresponding parts of the atlas. 
; The head and the atlas rotate together upon the axis, the pivot of rotation being the odontoid 
process, and the amount of rotation is limited by the check ligaments. No rotation can occur 
between the occiput and atlas, and 
stability between atlas and axis is 
best attained after a slight amount 
_ of rotation, similar to the oblique 
movement between occiput and 
atlas. 
External iateral ligament Vey 
(anterior and posterior parts) Wy 
} TEMPORO-MANDIBULAR 
; JOINT. 
This joint is an arthrodial 
diarthrosis. It occurs between 
the articular part of the glenoid 
fossa of the temporal bone and 
the condylar head of the 
mandible. These two articular 
_ surfaces aremarkedly dissimilar 
both in size and shape. In its 
general outline the articular 
surface of the head of the 
_ mandible is cylindrical, having 
its long axis directed from Stylo-mandibular ligament \ i 
within outwards and forwards. X \ 
On the other hand, the articular . 
part of the glenoid fossa in — 
front of the Glaserian fissure Fic. 204.—Temporo-MaNDIBULAR JOINT, 
is concavo-convex from behind 
forwards. Its articular surface includes the eminentia articularis, the eminence at 
the base of the anterior root of the zygoma. The articular surfaces of the bones 
are clothed by hyaline encrusting cartilage, whilst the joint cavity is divided into 
an upper and lower part by a meniscus of fibro-cartilage. 
Ligaments.—The joint is invested by a capsular ligament which is quite com- 
Styloid process 
MANDIBLE, 
