238 THE ARTICULATIONS 



sternal extremities. It results from this that when the ribs are raised, the centre 

 portion is thrust outward, somewhat after the fashion in which the handle of a 

 bucket is thrust away from the side when raised to a horizontal position, and 

 the lateral diameter of the chest is increased (see Fig. 162). The mobility of 

 the different ribs varies very much. The first rib is more fixed than the others, 

 on account of the weight of the upper extremity and the strain of the ribs beneath ; 

 but on the freshly dissected thorax it moves as freely as the others. From the 

 same causes the movement of the second rib is also not vei'y extensive. In the 

 other ribs this mobility increases successively down to the last two, which are very 

 movable. The ribs are generally more movable in the female than in the male. 



VII. Articulation of the Cartilages of the Ribs with the Sternum, 



etc. (Fig. 163). 



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

 dial joints, with the exception of the first, in which the cartilage is almost always 

 directly united with the sternum, and which must therefore be regarded as a 

 synarthrodial articulation. The ligaments connecting them are 



Anterior Chondro-sternal. Interarticular Chondro-sternal. 



Posterior Chondro-sternal. Anterior Chondro-xiphoid. 



Capsular. Posterior Chondro-xiphoid. 



The Anterior Chondro-sternal Ligament is a broad and thin membranous band 

 that radiates from the front of 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 downward, 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 Chondro-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. 



The Interarticular Chondro-sternal Ligaments. These are only found between 

 the second and third costal cartilages and the sternum. The cartilage of the 

 second rib is connected with the sternum by means of an inter articular 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. The cartilage of the 

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

 which is attached by one extremity to the cartilage of the third rib, and by the 

 other extremity to the point of junction of the second and third pieces of the 

 sternum. This articulation is provided with two synovial membranes. 



The Anterior Chondro-xiphoid. This is a band of ligamentous fibres Avhich 

 connects the anterior surface of the seventh costal cartilage, and occasionally also 

 that of the sixth, to the anterior surface of the ensiform appendix. It varies in 

 length and breadth in different subjects. 



The Posterior Chondro-xiphoid is a similar band of fibres on the internal or 

 posterior surface, though less thick and distinct. 



