Chnp.xxiv.j THE SPINE. 545 



dorso-lumbar region, moreover, the vertebrae, although 

 they have to support almost as much weight as have 

 those of the lumbar region proper, are yet dispropor- 

 tionately small in size. Being placed, also, near the 

 middle of the column, they can be influenced on all 

 sides by a powerful amount of leverage. The 

 gravity of all injuries to the spine depends upon the 

 risk of damage to the cord enclosed in the column. 

 Apart from this complication, fractures and disloca- 

 tions in this region are apt to do well, and if the 

 patient survive, the former lesions nearly always heal 

 readily. 



The position of the cord within the vertebral 

 canal and the arrangement of its membranes are such 

 that it presents many facilities for escaping injury 

 from violence. These will be dealt with subsequently 

 in speaking of the cord itself. It may, however, 

 be noted here that the construction of the vertebrae, 

 and their relation to one another, are of a character 

 to afford much protection to the cord, even in cases 

 where they themselves are extensively damaged. 

 " Being lodged in the centre of the column, it (the 

 cord) occupies neutral ground to forces which might 

 cause fracture. For it is a law in mechanics that when 

 a beam, as of timber, is exposed to breakage, and the 

 force does not exceed the limits of the strength of the 

 material, one division resists compression, another 

 laceration of the particles, while the third, between the 

 two, is in a negative condition." (Jacobson, Holmes' 

 "System "). Now, it happens that fractures of the spine 

 are most often due to violence that bends the column 

 forwards. The anterior segment, in such a case, will 

 be subject to compression, the posterior to laceration, 

 and the intermediate portion will be in a neutral con- 

 dition. When the spine is examined, it will be found 

 that its anterior part, composed of the large cancellous 

 bodies, is excellently adapted to resist the effects of 



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