132 ARTHROLOGY. 



from the superior part of the odontoid process, inside the ring of 

 the atlas, and may be regarded as a continuation of the superior 

 common ligament ; it divides into two strong bands, which become 

 attached on either side to roughened surfaces inside the neural 

 canal of the atlas. This portion is sometimes called the short 

 odontoid, while the long odontoid consists of smaller bands which 

 pass forwards and are attached inside the foramen magnum of the 

 occipital bone ; the latter ligament is also called the occipito- 

 axoid. The motion of this joint is purely rotatory, being in fact 

 the rotatory joint of the head ; or, in other words, when the head 

 rotates the atlas moves with it. 



Sacro-lwmhar Articulation. — This is formed by the last 

 lumbar and first sacral vertebrae. There are the usual typical 

 articulations between the centra and zygapophyses, and in 

 addition a pair of diarthroses formed by the facets on the trans- 

 verse processes, which exist and form joints also between the 

 fifth and sixth lumbar vertebrse (Fig. 60). The usual vertebral 

 ligaments are found, with the addition of a pair of capsular ones 

 for the transverse joints. t 



Coccygeal Articulations. — These are of the typical form, but 

 become more and more rudimentary as the bones lose more and 

 more the true vertebral character, the discs are formed, but the 

 ligaments become gradually blended, finally enveloping the bones 

 in a fibrous sheath. 



Thoracic Articulations. 



The thoracic skeleton contains the articulations which unite 

 the dorsal vertebrse to one another and to the ribs, those which 

 connect the ribs and costal cartilages, those joining the latter to 

 the sternum, and finally, those which connect the sternal 

 segments. We have already described the vertebral joints. 



Costo-vertebral Articulation. — A diarthrodial connection is 

 here formed by the head and tubercle of a rib, the juxtaposed 

 facets on the bodies df two dorsal vertebrse, and the transverse 

 process of the posterior one. The ligaments are as follows : — 

 The stellate or radiating ligament is situated inferiorly, and 

 consists of strong fibres, divided into three fasciculi, uniting the 

 head of the rib, one to the vertebra in front, a second to the 

 intervertebral disc, while the third passes to the posterior 

 vertebra ; the interarticular or round ligament passes from the 



