THE THORACIC WALL. 



93 



it follows that injudicious lacing is injurious to the thoracic and abdominal viscera. Transitory 

 pressure from without, however, may be very great without overcoming the normal elasticity 

 of the bony thorax.* Severe crushes of the chest may produce a laceration of the heart, of the 

 lungs, and of the liver without a concomitant fracture of the bony thorax. As a result of the 

 relative increase of lime salts, fractures of the bones of the thorax become more common with 

 advancing age. Prominence of definite portions of the bony thorax, arising from pressure from 

 within, may be produced by cardiac hypertrophy, by aortic aneurysm, by tumors, and by pleuritic 

 exudates. Localized flattenings and depressions may be brought about by pulmonary tuber- 

 culosis and by old pleuritic adhesions. Other deformities of the chest 

 are : The chicken breast of rachitis, in which the sternum projects ante- 

 riorly ;f the thoracic deformities of spinal curvature (kyphosis and 

 scoliosis); the flattened and narrow chest of phthisis, corresponding 

 more with the position during expiration; and the barrel-shaped chest 

 of emphysema, corresponding rather with the position, during inspiration. 



Sternal Region. In the sternal region the skin is but slightly 

 movable and the underlying connective tissue contains but little fat. 

 In the male the region is abundantly covered with hair. The deep 

 fascia is but poorly developed, as is also the case over the pectoralis 

 major. The greater the development of this muscle, the nearer are its 

 origins to the median line, and the more marked is the anterior median 

 furrow. 



The sternum is covered by the sternal membrane which is formed 

 by the fibers of the capsular ligaments of the sternocostal joints radiating 

 into the periosteum. The bone is characterized by the slight develop- 

 ment of the outer compact layers and by the preponderance of the 

 spongy substance. Pressure-atrophy is consequently easily produced 

 by tumors growing from within the chest or by aortic aneurysms. 

 Mediastinal abscesses may rupture through a sternal foramen (Fig. 41), 

 the presence of which is dependent upon a developmental disturbance. 

 These foramina, like the very rare congenital fissures of the sternum, are 

 also important from a medico-legal standpoint, since a comparatively 



_ A sternum 



slight trauma may produce a severe injury, particularly of the heart and with a foramen in the lower 



, . i 11 i ii_ i_ portion of the bodv of the 



of the great vessels. The synchondrosis which usually lasts throughout ne 



life between the manubrium and gladiolus is so firm that in fractures 



of the sternum (rare) in this vicinity pieces of bone almost always remain attached to the 



manubrium or gladiolus. 



The important artery of this region, the internal mammary, ramifies only in the thoracic 

 and abdominal walls, although it gives off small branches (such as the mediastinal and thymic 



* Circus performers apparently suffer no discomfort from having some one hammer upon an anvil placed upon 

 the chest. 



t The chicken breast stands in contrast to the rare funnel breast, in which the sinking in of the body of the st 

 is combined with a projection of the xiphoid process and of the costal margin. 



