166 SPECIAL ANATOMY OF THE SKELETON 



cave, and directed backward and downward, the first giving attachment to the 

 Sternothyroid, the third to the sixth inclusive to the Triangularis sterni, and 

 the six or seven inferior ones to the Transversalis muscle and the Diaphragm. 



Borders. Of the two borders, the superior border is concave, the inferior con- 

 vex; 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 ajnd tenth, 

 costal cartilages present small, smooth, oblong-shaped facets at the points where 

 they articulate. 



Extremities. Of the two extremities, the outer extremity 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, Sternothyroid, Pectoralis major, 

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

 Internal intercostals. 



Surface Form. The bones of the thorax are to a very considerable extent covered by mus- 

 cles, so that in the strongly developed muscular subject they are for the most part concealed. 

 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 median 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 (the sternal furrow) situated between 

 the two great pectoral muscles. 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 7 , 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 presternal notch, but the lateral parts of this border are 

 obscured by the tendinous origins of the Sternomastoid muscles, which present themselves 

 as oblique tendinous cords, which narrow and deepen the notch. Lower down on the sub- 

 cutaneous surface, a well-defined transverse ridge, the angulus Ludovici, is always to be felt. 

 This denotes the line of junction of the manubrium and the 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, it is easy to count downward and find any other. From 

 the middle of the sternum the furrow spreads out, and, exposing more of the surface of the 

 body of the bone, terminates below in a sudden depression, the infrasternal depression, or 

 pit of the stomach (scrobiculus cordis), which corresponds to the ensiform cartilage. This 

 depression lies between the cartilages of the seventh ribs, and in it the ensiform cartilage may 

 be felt. The sternum in its vertical diameter presents a general convexity forward, the most 

 prominent point of which is at the joint between the manubrium and gladiolus. 



On each side of the sternum the costal cartilages and ribs on the front of the thorax are par- 

 tially obscured by the great pectoral muscles, through which, however, they are to be felr as 

 ridges, with yielding intervals between them, corresponding to the intercostal spaces. Of these 

 spaces, the one between the second and third ribs is the widest, the next two somewhat nar- 

 rower, and the remainder, with the exception of the last two, comparatively narrow. 



The lower border of the Pectoralis major muscle corresponds to the fifth rib, and below 

 this, on the front of the thorax, the broad, flat outline of the ribs, as they begin to ascend, and 

 the more rounded outline of the costal cartilages, are often visible. The lower boundary of 

 the front of the thorax, the abdominothoracic arch, which is most plainly seen by arching 

 the body backward, is formed by the ensiform cartilage and the cartilages of the seventh, eighth, 

 ninth, and tenth ribs, and the extremities of the eleventh and twelfth ribs or their cartilages. 



On each side of the thorax, from the axilla downward, the flattened external surfaces of the 

 ribs may be defined in the form of oblique ridges, separated by depressions corresponding to the 

 intercostal spaces. They are, however, covered by muscles, which obscure their outline to a 

 certain extent in the strongly developed. Nevertheless, the ribs, with the exception of the first, 

 can generally be followed over the front and sides of the thorax without difficulty. The first rib, 

 being almost completely covered by the clavicle and scapula, can only be distinguished in a 



