212 THE ARTICULATIONS 



1. The Superior Intersternal Articulation. 



Class. — A mph iai'throsls. 



The lower border of the manubrium and the upper border of the body of 

 the sternum present oval-shaped, tlat surfaces, with their Ions axes transverse, and 

 covered with a thin layer of hyaline cartilage. An interosseous fibro-cartilage 

 is interposed between the bony surfaces: it corresponds exactly in shape and inti- 

 mately adlieres to them. At each lateral border this fibro-cartilage enters into the 

 formation of the second chondro-sternal articulation (fig. 217). In consistence it 

 varies, being in some cases uniform throughout, in others softer in the centre than 

 at the circumference, and in others again an oval-shaped synovial cavity is found 

 towards its anterior part. When such a ca^dty exists in the fibro-cartilage this 

 joint has a remote resemblance to the diarthrodes, and is classed, with the sacro-iliac 

 joint and the symphysis pubis under similar conditions, as ' diarthro-amphi- 

 arthrosis. ' 



The periosteum passes uninterruptedly over the joint from one segment of 

 the sternum to the other, forming a kind of capsular ligament. This capsule is 

 strengthened, especially on its posterior aspect, by longitudinal ligamentous fibres 

 as well as by the radiating and decussating fibres of the chondro-sternal ligaments. 



In some instances the fibro-cartilage is replaced by short bundles of fibrous 

 tissue which unite the cartilage-coated articular bony surfaces. 



2. The Inferior Intersternal Articulation. 



Class. — Syncirthrosis. 



The gladiolus is joined to the xiphoid cartilage by a thick investing membrane, 

 by anterior and posterior longitudinal fibres, and by radiating fibres of the sixth 

 and seventh chondro-sternal ligaments. The chondro-xiphoid ligament also 

 connects the xiphoid with the anterior surface of the sixth and seventh costal 

 cartilages, and thus indirectly Avith the gladiolus; and some fine fibro-areolar 

 tissue also connects the xiphoid with the back of the seventh costal cartilage. 



The junction of the xiphoid with the sternum is on a level somewhat posterior 

 to the junction of the seventh costal cartilage with the sternum. The union is 

 synarthrodial. 



{h) The Costo-chondral Joints 



Class . — Syna rth rosis. 



The extremity of the costal cartilage is received into a cup-shaped depression 

 at_ the end of the rib, which is somewhat larger than the cartilage. The two are 

 joined together by the continuity of the investing membranes, the periosteum of 

 the rib being continuous with the perichondrium of the cartilage, much in the same 

 way as the epiphyses of the bones are joined to their shafts. 



(c) The Chonduo-sternal Articulatioxs 



Class. — Diarthrost)^. Subdivision. — (linglymits. 



Tlu'se articulations are ])etween the lateral borders of the sternum and tlie ends 

 of the costal cartilages. The union of the first rib with the sternum is synarthrodial, 

 and tlierefore forms an exception to the others. From the second to the seventh 

 inclusive, the articulations have the following ligaments, which together form a 

 complete capsule:— 



Anterior chondro-sternal. Superior chondro-sternal. 



Posterior chondro-sternal Inferior chondro-sternal. 



