216 THE ARTICULATIONS OF THE HORSE 
coste) is a strong band which crosses the joint dorsally. It is attached on the 
vertebra above the costal facet and on the neck of the rib. 
Il. The costo-transverse articulation (Articulatio costo-transversaria). This 
is formed by the facet on the tubercle of the rib and on the transverse proc- 
ess of the vertebra. They are gliding joints. The capsule is reinforced by the 
dorsal costo-transverse ligament (Lig. 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 costw muscle, and begins to be 
quite distinct at the fifth joint. 
The cavity for the head of the first rib is formed by concave facets on the bodies of the last 
cervical and first thoracic vertebre. The conjugal ligament is absent, but the ligament of the 
neck is short and strong. ‘The radiate ligament is very strong, and consists of two parts. In the 
case of the last two or three ribs the costo-central and costo-transverse joints are confluent, and the 
various structures are correspondingly modified. 
Movements.—The chief movement is rotation around an axis which connects 
the centers of the head and tubercle of the rib. The movement is very limited in 
the anterior part of the series of joints, but very considerable in the posterior part. 
In the case of the first rib the movement is evidently extremely limited. The facet for the 
tubercle of the rib is deeply concave, and the axis of rotation is almost transverse, so that the 
movement is chiefly sagittal in direction. Further back the facets on the transverse processes 
become flat, and the axis of rotation gradually approaches a longitudinal direction. This, in 
connection with the mobility of the ventral ends of the asternal ribs and their elasticity, allows a 
great increase here in the range of movement which is largely transverse, the effect being to enlarge 
(chiefly) the transverse diameter of the thorax. 
COSTO-CHONDRAL ARTICULATIONS 
The costo-chondral junctions are synarthroses. The rib has a concave surface 
which receives the convex end of the cartilage. They are united by the continuity 
of the strong periosteum and perichondrium. 
CHONDRO-STERNAL ARTICULATIONS 
These joints (Articulationes sternocostales) are diarthroses formed by the 
junction of the cartilages of the sternal ribs with the sternum. The articular ends 
of the cartilages (except the first) are somewhat enlarged, and present surfaces of 
cylindrical curvature. The articular surfaces on the sternum fer the first pair of 
cartilages are placed close together on the dorsal border of the cariniform cartilage; 
the other seven are placed laterally at the Junctions of the segments. The capsules 
are strong and tight; the first pair of jomts has a common capsule, and the cartil- 
ages articulate with each other medially. The ventral ends of the first pair of ribs 
are firmly attached to each other by dense fibrous tissue, which is prolonged for- 
ward along the upper margin of the cariniform cartilage and is continuous behind with 
the sternal ligament. Each of the other capsules is reinforced dorsally by the radiate 
costo-sternal ligament (Ligamentum sterno-costale radiatum), composed of radi- 
ating fibers which blend with the sternal ligament. Interarticular bands may be 
present. The movement is rotation around a nearly vertical axis, except in the 
case of the first pair of joints. 
INTERCHONDRAL LIGAMENTS 
The eighth and ninth costal cartilages are firmly united by fibrous tissue. The 
chondro-xiphoid ligament attaches the ninth costal cartilage to the xiphoid carti- 
lage. The remaining cartilages are rather loosely attached to each other by elastic 
tissue. 
