200 ARTICULATIONS. 



neck of each rib, and the anterior surface of the adjacent transverse process. In 

 order fully to expose this ligament, a horizontal section should be made across 

 the transverse process and corresponding part of the rib ; or the rib may be 

 forcibly separated from the transverse process, and its fibres torn asunder. 



In the eleventh and twelfth ribs, this ligament is quite rudimentary. 



The Posterior Costo-transverse Ligament is a short, but thick and strong fasci- 

 culus, which passes obliquely from the summit of the transverse process to the 

 rough non-articular portion of the tubercle of the rib. This ligament is shorter 

 and more oblique in the upper than in the lower ribs. Those corresponding to 

 the superior ribs ascend, and those of the inferior ones slightly descend. 



In the eleventh and twelfth ribs, this ligament is wanting. 



The articular portions of the tubercle of the rib, and adjacent transverse pro- 

 cess, form an arthrodial joint, provided with a thin capsular ligament attached to 

 the circumference of the articulating surfaces, and inclosing a small synovial 

 membrane. 



In the eleventh and twelfth ribs, this articulation is wanting. 



Actions. The movement permitted in these joints is limited to a slight gliding 

 motion of the articular surfaces one upon the other. 



VI. ARTICULATION OF THE CARTILAGES OF THE RIBS WITH THE 



STERNUM. 



The articulations of the cartilages of the true ribs with the sternum are arthro- 

 dial joints. The ligaments connecting them are : 



Anterior Costo-sternal. 

 Posterior Costo-sternal. 

 Capsular. 



The Anterior Costo-sternal Ligament (fig. 126) is a broad and thin membranous 

 band that radiates from the inner extremity of the cartilages of the true ribs, to 

 the anterior surface of the sternum. It is composed of fasciculi, which pass in 

 different directions. The superior fasciculi ascend obliquety, the inferior pass 

 obliquely downwards, and the middle fasciculi horizontally. The superficial fibres 

 of this ligament are the longest ; they intermingle with the fibres of the ligaments 

 above and below them, with those of the opposite side, and with the tendinous 

 fibres of origin of the Pectoralis major ; forming a thick fibrous membrane, which 

 covers the surface of the sternum. This is more distinct at the lower than at the 

 upper part. 



The Posterior Costo-sternal Ligament* less thick and distinct than the anterior, 

 is composed of fibres which radiate from the posterior surface of the sternal end 

 of the cartilages of the true ribs, to the posterior surface of the sternum, becom- 

 ing blended with the periosteum. 



The Capsular Ligament surrounds the joints formed between the cartilages of 

 the true ribs and the sternum. It is very thin, intimately blended with the 

 anterior and posterior ligaments, and strengthened at the upper and lower part 

 of the articulation by a few fibres, which pass from the cartilage to the side of 

 the sternum. These ligaments protect the synovial membranes. 



Synovial Membranes. The cartilage of the first rib is directly continuous with 

 the sternum, the synovial membrane being absent. The cartilage of the second 

 rib is connected with the sternum by means of an interarticular ligament, attached 

 by one extremity to the cartilage of the second rib, and by the other extremity 

 to the cartilage which unites the first and second pieces of the sternum. This 

 articulation is provided with two synovial membranes. That of the third rib has 

 also two synovial membranes; and that of the fourth, fifth, sixth, and seventh, 

 each a single synovial membrane. Thus there are eight synovial cavities in the 

 articulations between the costal cartilages of the true ribs and the sternum. They 



