ARTICULATIONS OF THE RIBS AND STERNUM. 



131 



Fig. 120. 



Fig. 120. ARTICULATIONS OP THE 

 STERNUM, CLAVICLE AND RIBS, 



AS SEEN FROM BEFORE (after 



Arnold), 



On the right of the middle line 

 the anterior ligaments are shown ; 

 on the left side, the front parts of 

 the clavicle, sternum and costal 

 cartilages have been removed so as 

 to display the articular cavities. 

 1 to 10, the anterior extremities of 

 the ribs from the first to the tenth 

 inclusive, on the right side ; 1' to 

 10', the costal cartilages of the left 

 side from the first to the tenth in- 

 clusive ; at 1', the direct union of 

 the first costal cartilage with the 

 sternum is shown ; at the sternal 

 ends of the cartilages marked 2' to 

 6', the small double synovial cavi- 

 ties are shown opened ; between 

 the costal cartilages on the right 

 side, ligamentous bands are shown 

 stretching over the intercostal 

 spaces ; and on the left side, by a 

 section, small synovial cavities are 

 shown between the adjacent edges 

 of the intercostal cartilages from 

 the 5th to the 9th ; on the front 

 of the right half of the sternum 

 the radiating anterior costo-sternal 

 ligaments are shown ; 11, the ensi- 

 form process; 12, 12', the inter- 

 clavicular ligament; and below 12, 

 the anterior sterno- clavicular liga- 

 ment ; below 12', the sterno-clavi- 

 cular articulation is opened, showing 

 the interarticular fibro-cartilage and 

 double synovial cavity ; 13,thecosto- 

 clavicular or rhomboid ligament. 



Ligaments of the sternum. The manubrium, body, and xiphoid process 

 of the sternum, so long as they are not united by bone, are connected 

 by intervening cartilage, and by anterior and posterior ligaments ; and 

 the whole sternum is much strengthened by thick periosteum and by 

 the crossing and longitudinal bauds of the costo-sternal ligaments already 

 mentioned. 



MOVEMENTS OF THE RIBS. Each rib is capable of a certain amount of elevation 

 and depression at its vertebral articulation, and of rotation on an axis passing between 

 its vertebral and sternal ends. The heads of the ribs are, however, bound down by 

 the interarticular ligaments so tightly as to prevent any gliding motion at the 

 attachments of those ligaments, which may therefore be regarded as the fixed points 

 round which the ribs are moved. When the vertebral column is bent forwards, the ribs 

 are depressed ; and in the same manner, when the column is rotated, the ribs of that 

 side towards which the upper part of the trunk is turned are raised, and those of 

 the other side correspondingly depressed. The movement of the tubercle of the rib 

 on the transverse process is of a gliding description., in the circumference of a circle 

 of which the head of the rib is the centre ; and as the plane in which the opposed 

 surfaces of the costo-transverse articulation in most instances lies looks upwards and 

 backwards, the ribs are moved backwards as well as upwards in inspiration, and 

 forwards and downwards in expiration. The combined movements of the thoracic 

 walls in respiration will be described along with the actions of the intercostal 



K.2 



