244 THE ARTICULATIONS 



rosis covering the external intercostals. Its anterior surface is in relation with the 

 intercostal vessels and nerve; the posterior with the longissimus dor si. The 

 first rib has no (superior) costo-transverse ligament. 



The synovial membrane (fig. 281) is a single sac. 



The arterial and nerve supplies come from the posterior branches of the intercostal arteries 

 and nerves. 



The movements which take place at these joints are limited to a gliding of the tubercle of 

 the rib upon the transverse process. The exact position of the facet on the transverse process 

 varies slightly from above downward, being placed higher on the processes of the lower vertebrae. 

 The plane of movement in most of the costo-transverse joints is inclined upward and backward 

 in inspiration, and downward and forward in expiration. The point round which these move- 

 ments occur is the head of the rib, so that the tubercle of the rib glides upon the transverse 

 process in the circumference of a cncle, the centre of which is at the capitular joint. 



5. THE ARTICULATIONS AT THE FRONT OF THE THORAX 

 These may be divided into four sets, viz. : — 



(a) The interstemal joints, or the union of the several parts of the sternum 

 with one another. 



(6) The costo-chondral joints, or the union of the ribs with their costal 

 cartilages. 



(c) The chondro-stemal joints, or the junction of the costal cartilages with 

 the sternum. 



{d) The interchondral joints, or the union of five costal cartilages (sixth, 

 seventh, eighth, ninth, and tenth) with one another. 



(a) The Intersternal Joints 



The sternum being composed, in the adult, of three distinct pieces — the 

 manubrium, body, and the xiphoid process — has two articulations, viz., the 

 superior, which unites the manubrium with the body (gladiolus), and the inferior, 

 which unites the body with the xiphoid. 



1. The Superior Intersternal Articulation 

 C\a.ss.— False Synchondrosis. 



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

 sternum present oval-shaped, flat surfaces, with their long 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 

 intimately adheres to them. At each lateral border this fibro-cartilage enters 

 into the formation of the second chondro-sternal articulation (fig. 282). 



In consi.stence it varies, being in some cases uniform throughout, in others softer in the 

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

 toward its anterior part. When such a cavity exists in the fibro-cartilage this joint has a 

 remote resemblance to the diarthroses, and is classed, with the sacro-iliac joint and the symphy- 

 sis pubis under similar (conditions, as 'diarthro-amphiarthrosis.' 



The periostouin i)ass(!s uninterruptedly over the joint from one segment of the sternum to 

 the other, forming a kind of capsular ligament [inembraua sterni]. This capsule is strength- 

 ened, especially on its pos erior 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. — False Synchondrosis. 



The gladiolus is joined to the xiphoid cartilage by a thick investing mem- 

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

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

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

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

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



