THE THOKAX AS A WHOLE. 



113 



THE; COSTAL CARTILAGES. 



The costal cartilages, of which there are twelve pairs, are bars of hyaline cartilage 

 united to the anterior extremities of the ribs, into which they are recessed and held in 

 position by the periosteum. Through these cartilages the first seven ribs are con- 

 nected directly with the sternum by means of synovial joints corresponding to the 

 notches along the margins of the breast bone. To this there is an exception in the 

 case of the first rib, the cartilage of which is directly blended with the manubrium 

 sterni. The eighth, ninth, and tenth are connected indirectly with the sternum 

 by their union with each other, and their articulation, through the medium of 

 the eighth, with the seventh rib cartilage, whilst the eleventh and twelfth 

 cartilages tip the ribs to which they belong, and lie free in the muscles cf the 

 flank. The costal cartilages increase in length from the first to the seventh, 

 below which they become shorter. The first inclines obliquely downwards and 

 medially to unite with the superior angle of the manubrium. The second lies more 

 or less horizontally. The third to the seventh gradually become more and more 

 curved, inclining downwards from the extremities of their respective ribs, and then 

 turning upwards to reach the sternum. The tenth cartilage articulates by means of 

 a synovial joint with the 

 ninth, the ninth with the 

 eighth, and the eighth with 

 the seventh. There are also 

 surfaces for the articulation of 

 the seventh with the sixth, 

 and sometimes for the sixth 

 with the fifth. 



THE THORAX AS A 

 WHOLE. 



The bony and cartilaginous 

 thorax is barrel-shaped, being 

 narrower above than below, 

 and compressed from before 

 backwards. Its posterior wall 

 is longer than its anterior, and 

 its transverse width, which 

 reaches its maximum opposite 

 the eighth or ninth rib, is 

 much in excess of its sagittal 

 diameter. This is largely 

 owing to the forward projec- 

 tion of the thoracic part of 

 the vertebral column into the 

 thoracic cavity. 



The anterior wall is 

 formed by the ribs and rib 

 cartilages, together with the 

 sternum. The posterior wall 

 comprises the thoracic part of 

 the vertebral column and the 

 ribs as far as their angles. 

 Owing to the posterior curve 

 of the ribs, and the projection 

 forwards of the vertebral 

 bodies, the antero- posterior 



diameter of the thoracic cavity is considerably greater on each side of the median 

 plane than in the median plane, thus allowing for the lodgment of the rounded 



8 



FIG. 127. THE THORAX AS SEEN FROM THE RIGHT SIDE. 



