FEACTUEES OF EIBS. 109 



as in buffer accidents or squeezing in a crowd when the rib will 

 break at the point of maximum strain, as a rule slightly outside 

 the angle. 



In fracture by direct violence there is a tendency for the 

 broken ends to be driven inwards upon the underlying viscera, 

 particularly the lungs, whereas in fracture by indirect violence 

 the broken ends tend rather to be forced outwards, away from 

 the enclosed organs. Vertical displacement of the fragments is 

 prevented by the attachment of the intercostal muscles and 

 membranes. 



The adhesion of the parietal pleura to the inner surface of 

 the rib practically necessitates its laceration in every case of 

 fracture, and the passage of the upper division of the intercostal 

 artery along the subcostal groove indicates how rupture of this 

 vessel may occur. The blood from the artery will pass into the 

 tissues of the intercostal space and through the tear in the 

 parietal pleura into the pleural cavity, and may be so much in 

 amount as to give evidence of hsemothorax. 



The position of the intercostal nerve explains the reason 

 why pain in a fractured rib may be present at the site of fracture 

 and also referred to the extremity of the nerve. 



The close proximity of the lung, covered by the visceral 

 pleura, to the chest wall readily shows how easy it is for this 

 viscus to be injured. It may be bruised by the direct violence 

 which occasions the fracture, or lacerated by the broken ends 

 driven by that force into its superficial parts. The wound of the 

 lung causes haemorrhage, partly into the lung substance and 

 partly into the pleural cavity. The haemorrhage into the alveoli 

 and smaller bronchioles of the lung may be evidenced by 

 haemoptysis, but the expectoration of blood may be delayed for 

 some hours, on account of the length of the respiratory passages 

 through which it has to travel. 



During inspiration air may be drawn from the lacerated lung 

 tissue into the pleural cavity, and during expiration this air may 

 pass from the pleural cavity, across the wound in the parietal 

 pleura and between the fractured ends of the bone and torn 



