COSTO-TRANSVERSE ARTICULATIONS 



243 



(6) The Costo-transverse Articulation 



Class. — Diarthrosis. 



Subdivision. — Arthrodia. 



This joint is formed by the tubercle of the rib articulating with the anterior 

 part of the tip of the transverse process. The eleventh and twelfth ribs are 

 devoid of these joints, for the tubercles of these ribs are absent, and the transverse 

 processes of the eleventh and twelfth thoracic vertebrae are rudimentary. 



The ligaments of the imion are : — 



Articular capsule. 

 Neck ligament. 



Tubercular ligament. 

 Costo-transverse ligaments. 



The articular capsule (figs. 279 and 281) forms a thin, loose, fibrous envelope to 

 the synovial membrane. Its fibres are attached to the bones just beyond the 

 articular margins, and are thickest below, where they are not strengthened by 

 any other structure. It i s connected medially with the neck ligament, above 

 with the costo-transverse, and laterally with the tubercular (posterior costo- 

 transverse) ligaments. The eleventh and twelfth ribs are unprovided with costo- 

 transverse capsules. 



Fig. 281. — Horizontal Section through the Intervertebral Disc and Ribs. 



Fibrous ring of intervertebral 



fibro-cartilage 



Radiate ligament 



Capitnlar synovial 

 sac 



Pulpy nucleus of intervertebral 

 fibro-cartilage 



Costo-transverse synovial sac 



Tubercular ligament 



The neck ligament [lig. colli costse] (middle costo-transverse, or interosseous 

 ligament) (fig. 281), consists of short fibres passing between the back of the neck 

 of the rib and front of the transverse process, mt'h which the tubercle articulates. 

 It extends from the capsule of the capitular joint to that of the costo-transverse. 

 It is best seen on horizontal section through the bones. In the eleventh and 

 twelfth ribs this ligament is rudimentary. 



The tubercular ligament (posterior costo-transverse) (fig. 281) is a short but 

 thick, strong, and broad ligament, which extends laterally and upward from the 

 extremity of the transverse process to the non-articular surface of the tubercle 

 of the corresponding rib. The eleventh and twelfth ribs have no posterior 

 ligament. 



The (superior) costo-transvetse ligament (fig. 280) is a strong, broad band of 

 fibres which ascends laterally from the crest on the upper border of the neck 

 of the rib, to the lower border of the transverse process above, A few scattered 

 posterior fibres pass upward and medially from the neck to the transverse process. 

 The costo-transverse hgament is subdivided into a stronger anterior portion 

 (anterior costo-transverse hgament) best seen from the front (fig. 280), and a 

 weaker posterior portion (posterior costo-transverse ligament). Its medial 

 border bounds the foramen through which the posterior branches of the inter- 

 costal vessels and nerves pass. To the lateral border is attached the thin aponeu- 



