286 



THE ARTICULATIONS, OR JOINTS 



either their vertebral or sternal extremities. It results from this that when the ribs are raised, the 

 central 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 fl a horizontal position, and the lateral 



diameter of the thorax is increased (see 

 Fig. 236). The mobility of the different 

 ribs varies greatly. 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 very 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. 



VIE. Costosternal Articulations 

 (Articulationes Sternocostales) 



(Fig. 237). 



The articulations of the carti- 

 lages of the true ribs with the 

 sternum are arthrodial joints, with 

 the exception of the first, in which 

 the cartilage is almost always 

 directly united with the sternum, 

 and which must therefore be re- 

 garded as a synarthrodial articu- 

 lation. The ligaments connecting 

 them are the 



FIG. 236. Diagrams showing the axis of rotation of the 

 ribs in the movements of respiration. The one axis of rota- 

 tion corresponds with the line drawn through the two articula- 

 tions which the rib forms with the vertebral column (a, 6), and 

 the other with a line drawn from the head of the rib to the 

 sternum (A, B). (From Kirke's Handbook of Physiology.) 



Anterior Chondrosternal. 



Capsular. 



Posterior Chondrosternal. 



Intra-articular Chondrosternal. 



Chondroxiphoid. 



The anterior Chondrosternal ligament (ligamentum sternocostale radiatum) (Fig. 

 237) 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 fasciculi pass obliquely downward, and 

 the middle fasciculi pass 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 (membrana sterni). This is more distinct at the 

 lower than at the tipper part. 



The capsular ligament (capsula articularis) surrounds the joint formed between 

 the cartilage of a true rib 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 posterior Chondrosternal or sternocostal ligament (ligamentum sterno- 

 costale radiatum), less thick and distinct than the anterior, is composed of fibres 



