148 SURGICAL APPLIED ANATOMY. [Chap. x. 



thorax is very pliable and elastic, and if a constant 

 impediment exists to the entrance of air, as afforded, 

 for example, by greatly enlarged tonsils, the thoracic 

 walls may yield in time to the unbalanced pressure 

 brought to bear upon them at each inspiration. The 

 weakest part of the thorax is along the costo-chondral 

 line on either side, and it is here that the parietes 

 yield most conspicuously in such cases, and by this 

 yielding the deformity is produced." 



The sternum. The upper edge of the sternum 

 fin inspiration) corresponds to the disc between the 

 second and third dorsal vertebrse, and the sterno- 

 xiphoid joint to the lower part of the ninth dorsal. 

 A transverse ridge may be felt upon its anterior sur- 

 face that corresponds to the junction of the manu- 

 brium and gladiolus, and is in a line with the second 

 costal cartilages. The skin over the sternal region is 

 the part of the surface most frequently the seat of 

 keloid. The bone is rarely fractured, being soft 

 and spongy, and supported by the elastic ribs 

 and their cartilages, as by a series of springs. In 

 the old, when the cartilages are ossified and the chest 

 more rigid, the tendency to fracture is increased. 

 The sternum is most often found fractured in connec- 

 tion with injuries to the spine, although it may be 

 broken by simple direct violence. The bone may be 

 fractured by violent bending of the spine backwards, 

 and by abrupt bending of it forwards. In the former 

 instance the lesion is probably due to muscular 

 violence, to the abdominal muscles and the sterno- 

 mastoid pulling one against the other. In the latter 

 instance the lesion is commonly brought about 

 by the violent contact of the chin with the bone. In 

 all instances the fracture is usually transverse, and 

 most often occupies the line between the manubrium 

 and the gladiolus. As these two parts of the bone 

 are not entirely united until middle life, and are often 



