ABTICULATIONS OF THE THORAX. 141 



the head of the rib, and in diverging are carried over the bodies of the two 

 vertebras and the intervertebral disc. Lined above by the synovial mem- 

 branes, this ligament is covered below by the pleura. (Leyh includes a 

 capsular ligament for the head of the rib and another for the costal 

 tuberosity. He probably viewed the synovial membrane of these articula- 

 tions as such.) 



Synovial membranes. — Two in number, these are distinguished into 

 anterior and posterior, lying against each other, and separated in part 

 by the interarticular ligament they cover. Supported below by the stellate 

 ligament, above they are directly in contact with the small supercostal 

 muscles, and with vessels and nerves. 



CosTO-TRANSVBRSE ARTICULATIONS. — Afticular surfocBS. — In the rib, the 

 diarthrodial facet cut on the tuberosity. In the vertebra, the analogous 

 facet on the outside of the transverse process. 



Mode of union. — Two ligaments bind this articulation : 1, The posterior 

 costo-transverse ligament (Fig. 83, 4), a white fibrous band attached by its 

 extremities behind the tranverse process and the costal tuberosity, lined by 

 synovial membrane, and covered by the transverse insertions of several 

 spinal muscles ; 2, The anterior costo-transverse, or interosseous ligament 

 (Fig. 83, 8), a fasciculus of short, thick, white fibres, fixed on the anterior 

 surface of the transverse process near its base, and in the rugged excavation 

 on the neck of the rib. This ligament is invested, posteriorly, by the 

 synovial membrane, and covered in front by pads of adipose tissue which 

 separate it from the costo-vertebral articulation. 



Synovial membrane. — This is a small particular capsule kept apart from 

 the posterior synovial membrane of the costo-vertebral articulation by the 

 costo-transverse interosseous ligament. 



Chaeaotbrs peculiar to some Costo-vertebral Articulations. — 

 1. The first, and sometimes the second, costo-vertebral articulation has no 

 interosseous ligament, and only exhibits one synovial membrane. The 

 intervertebral cavity which concurs in forming the first is often excavated 

 between the last cervical and first dorsal vertebrse. 



2. The two or three last costo-transverse articulations are confounded 

 with the corresponding costo-vertebral joints. They have no proper serous 

 membrane, but the posterior synovial membrane of the latter is prolonged 

 around their articular surfaces. 



2. TJie Chondro-sternal or Gosto-sternal Articulations. 



{Preparation. — To show the articulation of the ribs with the cartilages, these with 

 the sternum, and the cartilages with each other, carefully remove the plem-a, the 

 triangular muscle of the sternum, the diaphragm, the transverse muscle of the abdomen, 

 then the pectorals, the great oblique, the transversalis of the ribs, and the intercostal 

 muscles.) 



The first eight ribs, in resting upon the sternum by the inferior extremity 

 of their cartilages, form eight similar arthrodial articulations. 



Articular surfaces. — Each sternal cartilage opposes_ to one of the lateral 

 cavities of the sternum the convex and oblong facet at its lower extremity. 



Mode of union.— The diarthrosis resulting from the union of these two 

 surfaces is enveloped everywhere by bundles of white, radiating, fibrous 

 tissue, which constitute a veritable ligamentous capsule. The superior part 

 of this capsule, known as the stellate or superior costo-sternal ligament, is 

 covered by the triangular (sterno-costalis internus) muscle ; it is joined 

 to a fibrous cord lying on the superior face of the sternum, and which 



