278 ARTICULATIONS. 



responding to the superior ribs ascend, and those of the inferior one slightly 

 descend. 



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



The articular portion of the tubercle of the rib, and adjacent transverse 

 process, 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 glid- 

 ing motion of the articular surfaces one upon the other. 



VII. ARTICULATION OF THE CARTILAGES OP THE RIBS WITH THE 

 STERNUM, ETC. (Fio. 193.) 



The articulation of the cartilages of the true ribs with the sternum are 

 arthrodial joints. The ligaments connecting them are : 



Anterior Costo-sternal. 

 Posterior Costo-sternal. 

 Capsular. 



The Anterior Costo-sternal Ligament 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 obliquely, 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, 

 becoming 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, without any synovial membrane. 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 ster- 

 num. 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 may be demonstrated by removing a thin section 

 from the anterior surface of the sternum and cartilages, as seen in the figure. 

 After middle life, the articular surfaces lose their polish, become roughened, 

 and the synovial membranes appear to be wanting. In old age, the articula- 

 tions do not exist, the cartilages of most of the ribs becoming continuous with 

 the sternum. The cartilage of the seventh rib, and occasionally also that of 

 the sixth, is connected to the anterior surface of the ensiform appendix, by a 

 band of ligamentous fibres, which varies in length and breadth in different 

 subjects. It is called the costo-xiphoid ligament. 



