192 THE ARTICULATIONS. 



cavity which concurs in forming the first is often excavated between the last 

 cervical and first dorsal vertebras. 



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. 



Intrinsic Articulations. 

 A. The Chondro-sternal or Costo-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 pleura, the triangularis 

 sterui muscle, the diaphragm, tlie 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 con- 

 stitute a veritable ligamentous capsule. The superior part of this capsule — known 

 as the stellate or superior costo-sternal ligament, is covered by the triangularis 

 sterui muscle ; it is joined to a fibrous cord lying on the superior face of the 

 sternum, and which is confounded in front with that of the opposite side. The 

 inferior portion — the irtferior stellate or costo-sternal ligament — is in relation 

 with the pectoral muscles. 



Synovial ccqysule. — There is one for each articulation. 



Characters proper to the first costo-sternal articulation. — The first costo-sternal 

 articulation is not separated from its fellow of the opposite side ; so that these two 

 joints are, in reality, only one, and the two cartilages lying close to each other 

 correspond by a small diarthrodial facet, continuous with that for the sternum. 

 The two sternal facets are inclined upwards, and confounded with one another. 

 Only one synovial cavity exists for this complex articulation, which unites the 

 two first ribs to each other and to the sternum. 



B. Chrondo-costal Articulations uniting the Ribs to their 



Cartilages. 



These are synarthrodial articulations, the movements of which are very 

 obscure. They are formed by the implantation of the cartilages in the nigged 

 cavities the ribs present at their inferior extremities. The solidity of these articu- 

 lations is assured by the adherence of the fibro-cartilages to the proper substance 

 of the ribs, and by the periosteum which, in passing from the bone to the cartilage, 

 plays the part of a powerful peripheral band. 



In the Ox, the sternal ribs, in uniting with their oartilages, form a true ginglymoid diar- 

 throsis, the movement of whicli is facilitated by a small synovial capsule. 



C. Articulations of the Costal Cartilages with each other. 



The ribs, attached to each other by means of the intercostal muscles, are not 

 united by real articulations ; neither are their cartilages of prolongation. But 



