ARTICULATIONS OF THE THORAX. 279 



rum,) is fixed, as its name expresses, in front of the joint. It 

 arises from the margin of the head of the rib by the whole 

 breadth of the latter, and diverging towards the spine, is fixed, 

 by its superior fibres, into the vertebra above; by its inferior 

 fibres, into the vertebra below; and, by its middle fibres, into 

 the inter-vertebral substance. It is a thin, flat, fibrous mem- 

 brane, leaving intervals in it for the passage of blood vessels, 

 and may, indeed, be considered as a capsule to the articula- 

 tion, and is frequently described as such. The inter-articular 

 ligament passes from the ridge on the head of the rib, to a cor- 

 responding line of the inter-vertebral substance. It is short 

 and strong, and divides the articulation of the head of the rib 

 into two cavities, which have no communication. It is in 

 consequence of the latter, that there are two synovial mem- 

 branes to the head of every rib which has a double articular 

 face; but the ribs which are articulated with a single vertebra, 

 as the first, the eleventh, and the twelfth, have not the inter- 

 articular ligament, and, therefore, only one synovial mem- 

 brane. 



The synovial membranes are not very apparent, neither is 

 the fluid abundant; the cavity is occasionally very small from 

 the encroachment of the inter-articular ligament. Anchylosis 

 occasionally takes place here, but it is much less frequent than 

 in the anterior articulations of the thorax. 



2. The Costo-transverse articulation has, in addition to the 

 joint formed between the tubercle of the rib and the end of the 

 transverse process, several ligamentous fasciculi which pass in 

 varied directions. 



Its synovial membrane is much more distinct than in the pre- 

 ceding articulation, and contains more synovia. The joint is 

 more loose, and is never anchylosed, except by disease. There 

 are a few fibres around it having the semblance of a capsule. 



The Internal Transverse Ligament (Ligamentum Transver- 

 sarium Internum, or Costo-Transversarium Inferius,) arises from 

 the inferior margin of the transverse process, between its root 

 and external extremity, and proceeding downwards and in- 

 wards, is inserted into the upper margin of the neck of the rib 

 below. In many of the ribs there is a plane of ligamentous 

 fibres parallel with this ligament, but just behind, and arising 



