246 



THE ARTICULATIONS 



and front ed^es of the articular surfaces separate a little; in expiration the reverse movement 

 takes place. Thus the two extremities of the costal arches move in their respective sockets in 

 opposite directions. 



This difference results necessarily from the fact that the costal arch moves upon the verte- 

 bral column, and, having been elevated, it in its turn raises the sternum by pushing it upward 

 and forward. 



The costo-xiphoid ligament tends to prevent the xiphoid cartilage from being drawn back- 

 ward b}' the action of the diaphragm. 



Fig. 282. — The Articulation at the Front of the Thorax. 

 (Left side, showing ligaments; right side, the synovial cavities.) 



For clavicle and first 



An interarticular 

 ligament 



Second rib 



The plate of fibro- 

 cartilage between 

 manubrium an 

 body 



Third rib 



Fourth rib 



Fifth rib -^j-V 



Sixth rib i?. 



Seventh rib 



Radiate sterno- 

 costal ligament 



Interchondral 

 capsular ligament 



Class. 



{d) The Interchondral Articulations 

 -Diarlhrosis. Subdivision. — Arthrodia. 



A little in front of the point wh(3re the costal cartilages bend upward toward 

 the median line the sixth is united with the seventh, tlie seventh with the eighth, 

 the eighth with the ninth, and the ninth with the tenth. 



At this point each of the cartilages from the sixth to the ninth inclusive is deeper than 

 fjsewhcre, owing to the projection downward from its lower edge of a broad blunt process, 

 which comes into contact with the curtilage next below. Each of the apposed surfaces is smooth, 



