262 THE ARTICULATIONS OR JOINTS. 
the upper and lower fasciculi proceed to the adjacent margins of the two vertebree 
between which the disc is situated, and with which the rib articulates. Toa slight 
extent these radiating fasciculi pass under cover of the lateral margin of the anterior 
common ligament of the vertebral bodies. In those joints in which the head of 
the rib does not articulate with an intervertebral disc, the central fasciculus of 
the stellate ligament is wanting, but the other two retain the same general 
arrangement. 
The interarticular ligament (lig. capituli costee interarticulare) consists of short 
transverse fibres within the capsule. These are attached, on the one hand, to 
the ridge which intervenes between the two facets on the head of the rib, and 
on the other to the lateral aspect of the intervertebral disc. This lgament 
is not a meniscus, but merely an interarticular ligament, of width sufficient 
to divide the joint cavity into an upper and a lower compartment. It is absent 
from those joints which do not articulate with an intervertebral disc, 2.e. from 
those ribs which only articulate with the body of one vertebra. 
The interarticular ligament is supposed to represent the outer end of a ligament which, 
under the name of the lig. conjugale costarum, connects the heads of the ribs of certain mammals 
across the posterior aspect of the intervertebral disc, and which, in the human subject, until the 
seventh month of foetal life, connects the posterior aspects of the necks of a pair of ribs across the 
mesial plane. 
Synovial membrane lines each joint cavity, and therefore, in all cases where the 
joint is divided into two compartments, each one has its own synovial membrane. 
Costo-TRANSVERSE JOINTS. 
The tubercle of each typical rib articulates with the transverse process of the 
lower of the two dorsal vertebree with which the head of the rib is associated 
(articulatio costo-transversaria). Near the tip of the transverse process there is 
an articular facet, on its anterior aspect, for articulation with the corresponding 
facet on the mesial articular part of the rib tubercle. The joint so formed is an 
arthrodial diarthrosis. 
The joint cavity is surrounded by a comparatively feeble capsular ligament, 
which is attached immediately beyond the margins of the articular facets, and in 
which no special bands can be distinguished. 
A simple synovial membrane lines the capsular ligament in all cases where the 
latter is present. 
The following accessory ligaments, in connexion with this joint, strengthen and 
support the articulation :— 
The anterior or superior costo-transverse ligament (ligamentum costo-transver- 
sarlum anterius, Fig. 199) consists of strong bands of fibres which are attached to 
the upper border of the neck of the rib, extending from the head outwards to the 
non-articular part of the tubercle. All these fibres*may be traced upwards. Those 
situated nearest to the head of the rib proceed obliquely upwards and outwards, to 
be attached to the transverse process immediately above, but with extensions to the 
adjoining rib and its costo-transverse capsular ligament. Others proceed almost 
vertically upwards to the adjoining transverse process, while those which ascend 
from the upper surface of the tubercle pass obliquely upwards and inwards to reach | 
the postero-inferior aspect of the adjoining transverse process. 
The posterior costo-transverse ligament (ligamentum costo-transversarium pos- 
terius) is a band of transverse fibres applied to the postero-external aspect of the 
capsule. By one end these fibres are attached to the tip of the transverse process 
behind its articular facet, and by the other to the external rough surface of the 
tubercle of the rib. 
The middle costo-transverse ligament (lig. colli coste) consists of short fibres 
which stretch from the posterior aspect of the neck of the rib, backwards and in- 
wards, to the front of the transverse process, but, in addition, a proportion of the 
fibres passes to the posterior aspect of the inferior articular process of the upper of 
the two vertebrae with which the head of the rib articulates. 
