ARTICULATIONS OF THE THORAX — COSTO-VERTEBRAL ARTICULATIONS 177 



atlas to the lower margin of the foramen magnum. It is narrower and thinner than 

 the superior membrane, and also fuses with the joint capsules. 



The lateral ligaments are two short bands which are partially blended with 

 the capsules. Each is attached to the border of the wnng of the atlas near the 

 intervertebral foramen, and to the outer surface of the paramastoid or styloid 

 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 verte])ral column, one by its head, 

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

 transverse joints. 



I. The costo-central articulations (Articulationes capitulorum) are trochoid 

 or rotatory joints, formed by the 



junction of the head of the rib 

 with the bodies of two adjacent 

 vertebrae and the intervertebral 

 fibro-cartilage. The two facets 

 on the head of the rib are separ- 

 ated by a non-articular groove, 

 and correspond to the two con- 

 cave facets (Fovese costales) on 

 the vertebral Ijodies. The cap- 

 sules are rather tight, and are 

 covered by the accessory liga- 

 ments, which are as follows: 1. 

 The radiate ligament (Ligamen- 

 tum capituli costie ratliatum) ex- 

 tends ventrally from the neck of 

 the rib to spread out on the 

 vertebral bodies and the inter- 

 vertebral fibro-cartilage. 2. The 

 conjugal ligament (Ligamentum 

 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 superior common ligament 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 attached to the intervertebral fibro- 

 cartilage. The joint cavity is divided into two compartments by the conjugal 

 ligament. 3. The ligament of the neck of the rib (Ligamentum colli costse) is 

 a strong band w^iich crosses the joint dorsally. It is attached on the vertebra 

 above the costal facet and on the neck of the rib. 



II. The costo-transverse articulations. These occur between the facets on 

 the tubercles of the ribs and those on the transverse processes of the vertebrae. 

 They are gliding joints. The capsule is reinforced by the superior costo-trans- 

 verse ligament (Ligamentum costo-transversarium dorsale), a distinct strong band 

 which arises on the transverse process and ends on the non-articular part of the 

 tubercle. It is covered by the levator costse muscle, and begins to be quite distinct 

 at the fifth joint. 



12 



Costo-lraJis- 



rerse ligament 

 Ligament of neck 

 Capsule 



Radiate ligament 

 Conjugal ligament 



Fig. 142.— Costo-vertebral Articulation, Anterior View. 

 (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



