THE COSTO-STERNAL ARTICULATIONS. 



143 



is much strengthened by thick periosteum, and by the radiating 

 bands of the costo-sternal ligaments already mentioned. 



Fig. 129. — Articul.\tions of the 

 Steenum, Clavicle, and Ribs, 

 as seen from before. (a. t. , 

 after Arnold. ) 5 



On the riglit of the middle line 

 the anterior ligaments are showTi ; 

 on the left side, the front parts of 

 the clavicle, sternum and costal 

 cartilages have been removed so as 

 to display the articular ca\'ities. 

 1 to 10, the anterior extremities of 

 the ribs from the first to the tenth 

 inclusive, on the right side ; 1' to 

 ICi', the costal cartilages of the left 

 side from the first to the tenth ; 

 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 spiovial cavities are shown 

 opened ; between the costal cartilages 

 on the right side, ligamentous bands 

 are shown stretching over the inter- 

 costal spaces ; and on the left side, 

 by a section, small syno^•ial cavities 

 are shown between the adjacent 

 edges of the intercostal, cartilages 

 from the fith to the 9th ; on the 

 front of the right half of the 

 sternum the radiating anterior costo- 

 stenial ligaments are shownti ; 11, 

 the ensiform process ; 12, 12', the 

 inter-clavicular ligament ; and be- 

 low 12, the anterior sterno-clavicu- 

 lar ligament ; below 12', the sterno- 

 clavicular articulation is opened, 

 ■showing the interarticular fibro- 

 cartilage and double synovial cavity ; 

 13, the costo-clavicular or rhomboid 

 ligament. 



Movements of the Ribs. — Each rib is capable of a certain amount of eleva- 

 tion and depression, 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 pomts round which the ribs are moved. TVTien the vertebral column 

 is bent foi-rvards, the ribs are depressed ; and when the column is rotated, 

 the ribs of that side towards which the upper part of the trunk is tmned 

 are raised, and those of the other side correspondingly depressed. The move- 

 ment of the tubercle of the rib on the transverse process is of a gliding 

 description, in the circumference of a cncle of which the head of the rib is the 

 centre ; and as the plane in which the ojiposed surfaces of the costo-transverse 

 articulation in most instances lie looks upwards and backwards, the ribs are 

 moved backwards as well as upwards m mspiration, and forwards and down- 

 wards in expiration. The combined movements of the thoracic walls in respira- 

 tion will be described along -with the actions of the intercostal muscles. It is 

 sufficient at present to state that the elevation and rotation of the ribs in mspi- 

 ration are the main causes of the antero-posterior and transverse enlargement 

 of the chest. The angular movement is greatest in the upper and least in the 

 lowest ribs. 



