'47 



part 5L 



CHAPTER X. 



THE THORAX. 



1. THE thoracic walls. The two sides of the 

 chest are seldom symmetrical, the circumference of 

 the right side being usually the greater, a fact that is 

 supposed to be explained by the unequal use of the 

 upper limbs. In Pott's disease, involving the dorsal 

 region, when the spine is much bent forwards, the 

 thorax becomes greatly deformed. Its antero-posterior 

 diameter is increased, the sternum protrudes, and may 

 even be bent by the bending of the spine, the ribs are 

 crushed together, and the body may be so shortened 

 that the lower ribs overlap the iliac crest. 



In pigeon-breast deformity the sternum and 

 cartilages are rendered protuberant, so that the antero- 

 posterior measurement of the chest is much increased, 

 while a deep sulcus exists on either side along the 

 line of junction of the ribs and their cartilages. It is 

 by the sinking in of the parietes along this line that 

 the protuberance is produced. Shaw gives the following 

 explanation of this deformity : " When an inspira- 

 tion is taken, a threatened vacuum is created within 

 the chest, air rushes in by atmospheric pressure, and 

 at the end of the inspiration the balance of pressure 

 without the chest and within it are equalised. If in 

 inspiration there is an impediment to the entrance of 

 air, the atmospheric pressure upon the external wall 

 of the chest must produce some effect, being un- 

 balanced by a like pressure upon the inner chest wall. 

 In children, and especially in rickety children, the 



