ARTICULATIONS OF THE THORAX—COSTO-VERTEBRAL ARTICULATIONS 215 
The joint surfaces are oblique, coming very close to the median line ventrally, but separated 
by a considerable interval dorsally. A triangular rough area cuts into the medial part of each of 
the atlantal articular surfaces. 
There are two roomy joint capsules, which sometimes communicate ventrally, 
especially in old subjects. 
The dorsal atlanto-occipital membrane (Membrana atlanto-occipitalis dorsalis) 
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 ven- 
tralis) extends from the ventral arch of the atlas to the ventral margin of the fora- 
men magnum. It is narrower and thinner than the dorsal membrane, and also 
fuses with the joint capsules. 
The lateral atlantal ligaments (Ligg. lateralia atlantis) are two short bands 
which are partially blended with the capsules. Each is attached to the border of 
the wing 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 
joint, formed by the junction of the 
head of the rib with the bodies of 
two adjacent vertebre and the 
intervertebral fibro-cartilage. The 
two facets on the head of the rib 
are separated by a non-articular 
grooye, and correspond to the two 
concave facets (Fovee costales) on 
the vertebral bodies. The joint 
capsule is rather tight, and is coy- 
ered by the accessory ligaments, 
which are as follows: 1. The radiate 
ligament (Lig. capituli costs 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 Fic. 233.—CosT0-VERTEBRAL ARTICULATION; ANTERIOR VIEW. 
a5 (After Schmaltz, Atlas d. Anat. d. Pferdes.) 
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 
__ Angle 
‘ 
&  Costo-trans- < 
SS verse ligament 
So Wigame nt of neck 
Capsule 
Radiate ligament 
Conjugal ligament 
