ARTICULATIONS OF THE THORAX— COSTO-VERTEBRAL ARTICULATIONS 215 



K,, . J^''-i°'°lf'^'i'^''® are oblique, coming very close to the median line ventrally but seDarate.l 



There are two roomy joint capsules, which sometimes communicate ventrallv 

 especially m old subjects. 



The dorsal atlanto-occipital membrane (Membrana atlanto-occipitalis dorsahs) 

 extends from the dorsal arch of the atlas to the dorsal margin of the foramen mag- 

 num. It IS blended with the capsules and contains many elastic fibers. 



The ventral atlanto-occipital membrane (Membrana atlanto-occipitalis veii- 

 tralis) extends from the ventral arch of the atlas to the ventral margin of the fora- 

 men magnum. It is narrower and thiimer than the dorsal membrane, and also 

 fuses with the joint capsules. 



The lateral atlantal Ugaments (Ligg. lateralia atlantis) are two short bands 

 which are partially blended %vith the capsules. Each is attached to the border of 

 the wmg of the atlas near the intervertebral foramen, and to the lateral surface of 

 the paramastoid process of the occipital bone. 



Movements.— These are chiefly flexion and extension. A small amount of 

 lateral oblique movement is also possible. 



Articulations of the Thorax 

 costo-vertebral articulations 



Each typical rib forms two joints with the vertebral column, one by its head, 

 and one by its tubercle. They are termed respectively costo-central and costo- 

 transverse joints. 



I. The costo-central articulation (Articulatio capituli) is a trochoid or rotatory 

 j oint, formed by the j unction of the 

 head of the rib with the bodies of 

 two adjacent vertebrae and the 

 intervertebral fibro-cartflage. The 

 two facets on the head of the rib 

 are separated by a non-articular 

 groove, and correspond to the two 

 concave facets (Fovese costales) on 

 the vertebral bodies. The joint 

 capsule is rather tight, and is cov- 

 ered by the accessory ligaments, 

 which are as follows : 1 . The radiate 

 ligament (Lig. capituli costse radi- 

 atum) extends ventrally from the 

 neck of the rib to spread out on 

 the vertebral bodies and the in- 

 tervertebral fibro-cartilage. 2. The 

 conjugal ligament (Lig. conjugale) 

 — absent from the first joint — is 

 attached to the groove on the head 

 of the rib, passes transversely into 

 the vertebral canal, and divides 

 under the dorsal longitudinal liga- 

 ment into two branches: one of these is attached to the body of the anterior vertebra; 

 the other is continued across to the head of the opposite rib, and is also attached to 

 the intervertebral fibro-cartilage. The joint cavity is divided into two compart- 

 ments by the conjugal ligament. 3. The ligament of the neck of the rib (Lig. colli 



Articular processes 



Transverse process 



-trans- 

 verse ligament 



■Ligament of neck 



Cajisiili' 

 \^Radiat(' ligiiment 



Conjugal ligament 



Fig. 233. — Costo-vektebral Articulation; Anterior View. 

 (After Schmaltz, Atlaa d. Aaat. d. Pferdes.J 



