THE THORAX 1043 



Ligaments. — ^These are as follows: posterior costo-transverse, 

 middle costo-transverse, superior costo-transverse, and capsular. 



The posterior costo - transverse ligament is a strong flat band, 

 situated on the posterior aspect of the joint, and extending from 

 the extremity of the transverse process to the non-articular part of 

 the tubercle of the rib. The direction of its fibres is upwards and 

 outwards. 



The middle costo-transverse or interosseous ligament consists of 

 short strong fibres which pass between the posterior surface of the 

 neck of the rib and the anterior surface of the adjacent transverse 

 process, namely, that with which the tubercle of the rib articulates. 

 Its fibres, which are disposed horizontally, extend from the costo- 

 central to the costo-transverse joint. This ligament is rudimentary 

 in the nth and 12th ribs. 



The superior costo-transverse ligaments are two in number, 

 anterior and posterior. The anterior ligament is a broad flat band, 

 external in position, the fibres of which pass from the crest on the 

 upper border of the neck of the rib to the lower border of the trans- 

 verse process immediately above, in the vicinity of its tip. Its 

 fibres are directed upwards and outwards, and its outer border is 

 continuous with the posterior intercostal aponeurosis. The pos- 

 terior ligament is a narrow band, internal to the preceding, and 

 extending from the back of the neck of the rib, below the crest, 

 to the lower aspect of the transverse process immediately above, 

 close to its base. 



The superior costo-transverse ligaments are wanting in the 

 case of the ist rib. 



The capsular ligament is formed in part by the posterior costo- 

 transverse ligament, and elsewhere by a thin loose membrane, the 

 fibres of which are attached external to the articular processes. It 

 is absent in the case of the nth and 12th ribs. 



The synovial membrane is single and small. 



Arterial and Nerve Supply. — Offsets from the posterior branches 

 of the intercostal arteries and nerves. 



The costo-transverse articulations are wanting in the case of 

 the nth and 12th ribs, and sometimes in the case of the loth. 



Costo-chondral Articulations. — These belong to the class syn- 

 arthrosis. The outer extremity of the costal cartilage is implanted 

 in the oval pit on the anterior extremity of the rib, and the union 

 is effected by the continuity which takes place between the peri- 

 osteum of the rib and the perichondrium of the cartilage. 



2. Costal Cartilages — Chondro-sternal Articulations. — ^These belong 

 to the class diarthrosis, and to the subdivision ginglymus, except in 

 the case of the ist joint, which belongs to the class synarthrosis. 

 The cartilages which take part in these joints are the first seven 

 on either side, these being received into the costal pits or facets on 

 the side of the sternum. 



The ligaments are anterior, posterior, superior, and inferior, 

 and, in the case of the 2nd joint at least, interarticular. 



