112 LIGAMENTS OF THE RIBS. 



which the mouth is opened ; elevation, by which it is closed; a for- 

 ward and backward movement, and a movement from side to side. 



In the movement of depression the interarticular cartilage glides 

 forwar dson the eminentia articularis, carrying with it the condyle. 

 If this movement be carried too far, the superior synovial membrane 

 is -ruptured, and dislocation of the fibre-cartilage with its condyle 

 into the zygomatic fossa occurs. In elevation the fibro-cartilage 

 and condyle are returned to their original position. The forward 

 and backward movement is a gliding of the fibro-cartilage upon the 

 glenoid articular surface, in the antero-posterior direction ; and the 

 movement from side to side, in the lateral direction. 



6. Articulation of the Ribs with the Vertebra. The ligaments of 

 these articulations are so strong as to render dislocation impossible, 

 the neck of the rib would break before displacement could occur ; 

 they are divisible into two groups : 1. Those connecting the head 

 of the rib with the vertebra ; and 2. Those connecting the neck and 

 tubercle of the rib with the transverse processes. They are 



1st Group. 



Anterior costo-vertebral or stellate, 



Capsular, 



Interarticular ligament, 



Two synovial membranes. 



2d Group. 



Anterior costo-transverse, 

 Middle costo-transverse, 

 Posterior costo-transverse. 





The anterior costo-vertebral or stellate ligament (fig. 39) consists 

 of three short bands of ligamentous fibres that radiate from the 

 anterior part of the head of the rib. The superior band passes 

 upwards, and is attached to the vertebra above ; the middle fasci- 

 culus is attached to the inter vertebral substance ; and the inferior, 

 to the vertebra below. 



In the first, eleventh, and twelfth ribs, the three fasciculi are 

 attached to the body of the corresponding vertebra. 



The capsular ligament is a thin layer of ligamentous fibres sur- 

 rounding the joint in the interval left by the anterior ligament ; it is 

 thickest above and below the articulation, and protects the synovial 

 membranes. 



The interarticular ligament passes between the sharp crest on the 

 head of the rib and the intervertebral substance. It divides the joint 

 into two cavities, which are each furnished with a separate synovial 

 membrane. The first, eleventh, and twelfth ribs have no interarticular 

 ligament, and consequently but one synovial membrane. 



The anterior costo-transverse ligament is a broad band composed 



