184 



THE A R TIC I 'LA TIOXS 



Thv arterial siipj.lv is dcrivi'd from twijis of the vi'rtel)ral, and occasionally 

 from twiiis Iroin the meningeal hranches of tlie ascending i)haryngeal. 



Thr nerve-supply eonies from the anterior division of the suboccipital nerve. 



Movements.— Bv the symmetrical and bilateral arrangement of these joints, 

 security and strength" are gained at the exi)ense of a very small amount of actual 

 articular surface; the basis of sui)i)ort and the area of action being equal to the 

 width between the most distant l>orders of the joint. 



The jirincipal movement permitted at these joints is of a ginglymoid character, 

 producing flexion and extension upon a transverse axis drawn across the condyles 

 at their slightlv constricted parts. 



In flexion," the forehead and chin drop, and what is called the nodding move- 

 ment is made; in extension, the chin is elevated and the forehead recedes. 



Fig. 194.— Axtekiok View of thk Upper End of the Spine. 



The anterior oblique 

 or lateral oecipito- 

 atlautal ligament 



Atlanto-axoidean 

 capsular ligament 



Capsular ligaments ot 

 articular piocesses 

 between axis and 

 the third, the third < 

 and fourth, and the 

 fourth and fifth cer- 

 vical vertebrae 



Continuation of 

 the anterior 

 common liga- 

 ment of the 

 vertebral 

 column 



Anterior oeeipi- 

 to-atlantal 

 ligament 



Anterior atlanto- 

 axoidean ligament 



Short vertebral 

 ligament 



Anterior common 

 ligament 



There is also a slight amount of gliding niovcnicnt, either directly lateral, the 

 outer edge of one condyle sinking a little within the outer edge of the socket of the 

 atlas, and that of tlie opposite con<lyle ]n'ojecting to a corresponding degree. The 

 head is thus tilted to one side, and it is even i)ossil)le that the Aveight of the skull 

 may l^e borne almost entirely on one joint, the articular surfaces of the other being 

 thrown out of ('(jntact. 



Or the movement may l)e obliquely lateral, when the lower side of the head 

 will be a trifle in advance ()f the elevated side. In this motion, which takes place 

 on the antero-])osterior axis, one condyle advances slightly and approaches the 

 middle line, while the oth.T recedes. "This is of the nature of rotation, though 

 there is no true rotation lound a vertical axis possible between the occiput and 

 atlas. 



These lateral movements are checked by the lateral odontoid ligaments and the 



