DISSECTION OF THE BACK AND THORAX. 133 



The Inter articular Ligament is fixed to the groove dividing the articular 

 head of the rib into two facets. It passes inwards across the floor of 

 the spinal canal, being united to the upper edge of the intervertebral 

 disc ; and on the middle line it becomes continuous with the corre- 

 sponding ligament of the opposite rib. It is not present in the 1st rib. 

 It should be displayed by disarticulating the costo-transverse joints of 

 the first vertebra in the segment, and then removing the arch. On 

 removing the superior common ligament, it will be found in the interval 

 between the two vertebral bodies. 



Synovial Sacs. — There is one sac on each side of the interarticular 

 ligament. There is only one sac for the first costo-central joint. 



CosTO-TRANsvERSE JoiNT. This is maintained by two ligaments — an 

 anterior and a posterior costo-transverse ligament, and it possesses a 

 synovial sac. 



Fig. 14. 



Two COSTO-VERTEBRAL, AND TWO INTERVERTEBRAL JOINTS, VIEWED FROM ABOVE. ThE LaMIN^ 



OF THE Vertebra have been removed. 

 1. Posterior costo-transverse ligament ; 2. Anterior (interosseous) costo-transverse ligament 

 3, 3. Superior common ligament. 



The Postei'ior Costo-transverse Ligament is composed of a band of 

 fibres stretching across the joint behind, and fixed by its extremities to 

 the rib and transverse process. 



The Anterior {Interosseous) Costo-transverse Ligament stretches between 

 the antero-inferior aspect of the transverse process and the neck of 

 the rib. It is partly concealed by the transverse process, and is best 

 seen when viewed from above and in front. 



Synovial Sac. — This will be exposed by removing the posterior costo- 

 transverse ligament. In the last two or three ribs there is no separate 

 synovial sac for the costo-transverse joint ; but the posterior costo- 

 central sac is extended over it, the two articular surfaces being in 

 these ribs continuous. 



