236 THE SKELETON. 



The Costal Cartilages. 



The Costal Cartilages (Fig. 179, p. 230) are white, elastic structures, 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 car- 

 tilages of the last two ribs, which have pointed extremities, float freely 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, whilst all the 

 rest follow the course of the ribs for a short extent, and then ascend to the sternum 

 or preceding cartilage. Each costal cartilage 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 attach- 

 ment 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, and the six or seven inferior ones affording attachment to the 

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

 concave, the inferior convex : they afford attachment to the 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 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 costal cartilage, 



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



