144 



LIGAMENTS OF THE RIBS. 



Fig. 81 * 



Besides the lower jaw, there are several other joints provided with u 



complete interarticular cartilage, and, con 

 sequently, with two synovial membranes; 

 they are, the sterno-clavicular articulation, 

 the acromio-clavicular and the articulation, 

 of the ulna with the cuneiform bone. 



The interarticular fibrous cartilages of 

 the knee-joint are partial, and there is but 

 one synovial membrane. 



The articulations of the heads of the 

 ribs with the ^vertebra have two synovial 

 membranes, separated by an interarticular 

 ligament, without fibrous cartilage. 

 Actions. The movements of the lower jaw are depression, by which 

 the mouth is opened ; elevation, by which it is closed ; a forward and 

 backward movement, and a movement from side to side. 



In the movement of depression, the interarticular cartilage glides for- 

 wards on 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 fibro-cartilage with its condyle into the zygomatic 

 fossa occurs. In elevation, the fibrous 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 bodies 

 of 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, 



2d Group. 



Anterior costo-transverse, 

 Middle costo-transverse, 

 Posterior costo-transverse. 



The anterior costo-vertebral or stellate ligament (fig. 72) 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 

 10 the vertebra above : the middle fasciculus is attached to the interVerte- 

 bral substance ; and the inferior, to the vertebrae below. 



* In this sketch a section has been carried through the joint, in order to show the 

 natural position of the interarticular fibro-cartilage, and the manner in which it is 

 adapted to the difference of form of the articulating surfaces. 1. The glenoid fossa. 

 2. The eminentia articularis. 3. The interarticular fibro-cartilage. 4. The superior 

 synovial cavity. 5. The inferior synovial cavity. 6. An interarticular fibro-cartilage, 

 removed from the joint, in order to show its oval and concave form j it is seen from 

 below 



Interarticular ligament, 

 Two synovial membranes 



