Chap, x.] THE THORAX. 149 



not united at all, it follows that the lesion is in many 

 cases a dislocation rather than a fracture. The manu- 

 brium in these injuries 'generally remains in situ, 

 while the gladiolus with the ribs is displaced forwards 

 in front of it. Malgaigne cites the case of a youth 

 who, from constant bending at his work as a watch- 

 maker, caused the second piece of the sternum to 

 glide backwards behind the manubrium. Here, prob- 

 ably, the connection between the two bones was not 

 very substantial. 



From its exposed position and cancellous structure, 

 the sternum is liable to many affections, such as caries 

 and gummatous periostitis. The comparative softness 

 also of the bone is such that it has been penetrated by 

 a knife in homicidal wounds. The shape and position 

 of the bone have also been altered by pressure, as 

 seen sometimes in artisans following employments re- 

 quiring instruments, etc., to be pressed against the 

 chest. 



Certain holes may appear in the middle of the 

 sternum, and through them mediastinal abscesses may 

 escape, and surface abscess pass deeply into the thorax. 

 In the case of E. Groux, the bone was separated verti- 

 cally into two parts. The gap could be opened by 

 muscular effort, and the heart exposed covered only 

 by the soft parts. The sternum has been trephined 

 for mediastinal abscess, and for paracentesis in peri- 

 cardial effusion, and it has been proposed also to 

 ligature the innominate artery through a trephine hole 

 in the upper part of the bone. 



The ribs are placed so obliquely that the anterior 

 end of one rib is on a level with the posterior end of 

 a rib some way below it in numerical order. Thus 

 * the first rib in front corresponds to the fourth rib 

 behind, the second to the sixth, the third to the 

 seventh, the fourth to the eighth, the fifth to the ninth, 

 the sixth to the tenth, and the seventh to the eleventh. 



