316 



THE AETICULATIONS OE JOINTS. 



of the sixth and seventh cartilages, the joint cavity is always small, and is frequently 

 obliterated. 



The sternal end of each of these costal cartilages presents a slight antero-pos- 

 terior ridge which fits into a shallow V-shaped depression upon the lateral margin 

 of the sternum. With the exception of the sixth cartilage, they articulate opposite 

 the lines of union between the primary segments of the sternum ; the sixth articu- 

 lates upon the side of the lowest segment of the body of the sternum. 



Each joint is enclosed by a capsula articularis, the fibrous stratum of which is 

 attached to the adjacent borders of the articulating elements. Specially strong 

 fibres distinguish the superficial and deep aspects of the capsule. 



The lig. sternocostale radiatum (O.T. anterior costo-sternal ligament) (Fig. 301) is 

 composed of strong fibres which radiate from the anterior surface of the costal 

 cartilage, near its sternal end, to the front of the sternum. The ligaments of 

 opposite sides interlace with each other, and so cover the front of the sternum with 

 a felted membrane the membrana sterni. 



Costo-clavicular 

 ligament 



Anterior sterno-clavicular 

 ligament 



Joint capsule 

 Joint cavity 



Interarticular ligament 



Joint cavity 



sterno-costale radiatum 



FIG. 301. STERNO-CLAVICULAR AND STERNO-COSTAL JOINTS. 



The lig. sternocostale posterius (posterior costo-sternal ligament) also a part 

 of the capsule has attachments similar to the foregoing, but the arrangement of 

 its fibres is not so powerful. 



The ligamentum costoxiphoideum passes from the front of the upper part of the 

 xiphoid process, obliquely upwards and laterally to the front of the seventh, and 

 sometimes to the front of the sixth costal cartilage. 



Within the capsules of these joints ligamenta sternocostalia interarticularia (inter- 

 articular ligaments) (Fig. 301) may be found. Their disposition is somewhat uncertain, 

 for whereas, in the case of the second pair of cartilages, they invariably divide the 

 joint cavity into two distinct compartments an upper and a lower such an 

 arrangement is very uncertain in the other joints, and they occasionally, especially 

 in the cases of the sixth and seventh cartilages, entirely obliterate the joint cavity. 

 These ligaments extend horizontally between the ends of the costal cartilages and 

 the side of the sternum. 



The stratum synoviale is found wherever a joint cavity is developed, and there- 

 fore there may be one or two synovial strata, according to the presence or absence 

 of a proper interarticular ligament. When the joint cavity is obliterated by the 

 fibrous structure which represents the interarticular ligament, a synovial stratum 

 is also absent. 



