DISSECTION OP THE BACK AND THORAX. 133 



h.^tflZ'^'^i^'' ^^^»'^^«i«fi^edtothe groove dividing the articular 

 head of the nb intoHwo facets. It passes inwards across the floor of 

 tV^Tl '^T,^' b«ing united to the upper edge of the intervertebral 

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

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

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

 the farst vertebra in the segment, and then removing the arch On 

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

 between the two vertebral bodies. 



Synovial Sacs.~Theve is one sac on each side of the interarticular 

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



CosTO-TBANSVBHSE JoiNT. This ia maintained by two hgaments-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 VERTEBR.E HAVE BEEN REMOVED, 



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

 3, 3. Superior common ligament. 



The Posterior 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. 



