THE COSTAL CARTILAGES. 133 



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 infmsternal depression or pit of the stomach (scro- 

 btculus cordis), which corresponds to the ensiform cartilage. This depression lies between the 

 cartilages of the seventh rib, 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 chest are par- 

 tially obscured by the great pectoral muscle ; through which, however, they are to be felt 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 chest, 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 abdomino-thoracic 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 chest, 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 chest without difficulty. The first rib, 

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

 portion of its extent. At the back the angles of the ribs form a slightly-marked oblique line on 

 each side of and some distance from the vertebral spines. This line diverges somewhat as it 

 descends, and external to it is a broad, convex surface caused by the projection of the ribs 

 beyond their angles. Over this surface, except where covered by the scapula, the individual 

 ribs can be distinguished. 



Surgical Anatomy. Malformations of the sternum present nothing of surgical importance 

 beyond the fact that abscesses of the mediastinum may sometimes escape through the sternal 

 foramen. Fractures of the sternum are by no means common, owing, no doubt, to the elasticity 

 of the ribs and their cartilages, which support it like so many springs. When broken it is fre- 

 quently associated with fracture of the spine, and may be caused by forcibly bending the body 

 either backward or forward until the chin becomes impacted against the top of the sternum. It 

 may also be fractured by direct violence or by muscular action. The fracture usually occurs in 

 the upper half of the bod.y of the bone. Dislocation of the gladiolus from the manubrium also 

 takes place, and is sometimes described as a fracture. 



The bone, being subcutaneous, is frequently the seat of gummatous tumors, and not uncom- 

 monly is affected with caries. Occasionally the bone, and especially its ensiform appendix, becomes 

 altered in shape and driven inward by the pressure, in workmen, of tools against their chest. 



The ribs are frequently broken, though from their connections and shape they, are able to 

 withstand great force, yielding under the injury and recovering themselves like a spring. The 

 middle of the series are the ones most liable to fracture. The first, and to a less extent the 

 second, being protected by the clavicle, are rarely fractured ; and the eleventh and twelfth, on 

 account of their loose and floating condition, enjoy a like immunity. The fracture generally 

 occurs from indirect violence, from forcible compression of the chest-wall, and the bone then 

 gives way at its weakest part i. e. just in front of the angle. But the ribs may also be broken 

 by direct violence, when the bone gives way and is driven inward at the point struck, or they 

 may be broken by muscular action. It seems probable, however, that in these latter cases the 

 bone has xmdergone some atrophic changes. Fracture of the ribs is frequently complicated with 

 some injury to the viscera contained within the thorax or upper part of the abdominal cavity, 

 and this is most likely to occur in fractures from direct violence. 



Fracture of the costal cartilages may also take place, though it is a comparatively rare injury. 



The thorax is frequently found to be altered in shape in certain diseases. 



The rickety thorax is caused chiefly by atmospheric pressure. The balance between the air 

 on the inside of the chest and the outside during some stage of respiration is not equal, the pre- 

 ponderance being in favor of the air outside ; and this, acting on the softened ribs, causes them 

 to be forced in at the junction of the cartilages with the bones, which is the weakest part. In 

 consequence of this the sternum projects forward, with a deep depression on either side caused 

 by the sinking in of the softened ribs. The depression is less on the left side, on account of 

 the ribs being supported by the heart. The condition is known as "pigeon-breast." The 

 lower ribs, however, are not involved in this deformity, as they are prevented from falling in by 

 the presence of the stomach, liver, and spleen. And when the liver and spleen are enlarged, 

 as they sometimes are in rickets, the lower ribs may be pushed outward : this causes a trans- 

 verse constriction just above the costal arch. The anterior extremities of the ribs are usually 

 enlarged in rickets, giving rise to what has been termed the ''rickety rosary." The phthisical 

 chest is often long and narrow, flattened from before backward, and with great obliquity of the 

 ribs and projection of the scapulae. In pulmonary emphysema the chest is enlarged in all its 

 diameters, and presents on section an almost circular outline. It has received the name of the 



