132 THE SKELETON. 



The Costal Cartilages. 



The Costal Cartilages (Fig. 79, p. 126) are bars of white, hyaline cartilage, 

 which serve to prolong the ribs forward to the front of the chest, and contribute 

 very materially to the elasticity of its walls. The first seven are connected with 

 the sternum, the next three with the lower border of the cartilage of the preceding 

 rib. The cartilages of the last two ribs have pointed extremities, which 

 terminate in free ends in the walls of the abdomen. Like the ribs, the costal 

 cartilages vary in their length, breadth, and direction. They increase in length 

 from the first to the seventh, then gradually diminish to the last. They diminish 

 in breadth, as well as the intervals between them, from the first to the last. They 

 are broad at their attachment to the ribs, and taper toward their sternal extremities, 

 excepting the first two, which are of the same breadth throughout, and the sixth, 

 seventh, and eighth, which are enlarged where their margins are in contact. In 

 direction they also vary : the first descends a little, the second is horizontal, the 

 third ascends slightly, while all the rest follow the course of the ribs for a short 

 extent, and then ascend to the sternum or preceding cartilage. Each costal carti- 

 lage presents two surfaces, two borders, and two extremities. The anterior surface 

 is convex, and looks forward and upward : that of the first gives attachment to the 

 costo-clavicular ligament and the Subclavius muscle ; that of the second, third, 

 fourth, fifth, and sixth, at their sternal ends, to the Pectoralis major. 1 The others 

 are covered by, and give partial attachment to, some of the great flat muscles of the 

 abdomen. The posterior surface is concave, and directed backward and downward, 

 the first giving attachment to the Sterno-thyroid, the third to the sixth inclusive 

 to the Triangularis sterni, and the six or seven inferior ones to the Tranversalis 

 muscle and the Diaphragm. Of the two borders, the superior is concave, the 

 inferior convex : they afford attachment to the internal Intercostal muscles, the 

 upper border of the sixth giving attachment to the Pectoralis major muscle. 

 The contiguous borders of the sixth, seventh, and eighth, and sometimes the ninth 

 and tenth, costal cartilages present small, smooth, oblong-shaped facets at the 

 points where they articulate. Of the two extremities, the outer one is continuous 

 with the osseous tissue of the rib to which it belongs. The inner extremity of the 

 first is continuous with the sternum ; the six succeeding ones have rounded 

 extremities, which are received into shallow concavities on the lateral margins of 

 the sternum. The inner extremities of the eighth, ninth, and tenth costal cartilages 

 are pointed, and are connected with the cartilage above. Those of the eleventh and 

 twelfth are free and pointed. 



The costal cartilages are most elastic in youth, those of the false ribs being 

 more so than the true. In old age they become of a deep yellow color, and are 

 prone to calcify. 



Attachment of Muscles. To nine : the Subclavius, Sterno-thyroid. Pectoralis 

 major, Internal oblique, Transversalis, Rectus, Diaphragm, Triangularis sterni, and 

 Internal intercostals. 



Surface Form. The bones of the chest are to a very considerable extent covered by 

 muscles, so that in the strongly-developed muscular subject they are for the most part con- 

 cealed. In the emaciated subject, on the other hand, the ribs, especially in the lower and lateral 

 region, stand out as prominent ridges with the sunken, intercostal spaces between them. 



In the middle line, in front, the superficial surface of the sternum is to be felt throughout 

 its entire length, at the bottom of a deep median furrow situated between the two great pectoral 

 muscles and called the sternal furrow. These muscles overlap the anterior surface somewhat, so 

 that the whole of the sternum in its entire width is not subcutaneous ; and this overlapping is 

 greater opposite the centre of the bone than above and below, so that the furrow is wider at its 

 upper and lower parts, but narrower in the middle. The centre of the upper border of the ster- 

 num is visible, constituting the pre-sternal notch, but the lateral parts of this border are obscured 

 by the tendinous origins of the Sterno-mastoid muscles, which present themselves as oblique 

 tendinous cords, which narrow and deepen the notch. Lower down on the subcutaneous surface 

 a well-defined transverse ridge, the angle of Ludovic, is always to be felt. This denotes the line 

 of junction of the manubrium and body of the bone, and is a useful guide to the second costal 

 cartilage, and thus to the identity of any given rib. The second rib being found through its 

 1 The first and seventh also,' occasionally, give origin to the same muscle. 



