chap, xxiv.] THE SPINE. 513 



It is in these parts of the cord that the main motor 

 tracts run, and thus it happens that motion is more 

 often lost in the parts below the site of the injury 

 than is sensation. If there be partial motor and 

 sensory paralysis, the disturbance of the former 

 function is likely to be in excess of that of the latter. 

 In no case, indeed, does there appear to have been a 

 loss of sensation without, at the same time, some 

 disturbance in the powers of movement. If the grey 

 matter .of the cord be not severely damaged, reflex 

 movements appertaining to that segment of the cord 

 can usually be induced in the paralysed parts by 

 proper stimulation. If those reflex movements be 

 lost, it may be inferred that the grey matter is broken 

 up, and that the entire spinal medulla has been 

 crushed at the seat of lesion. 



The higher up the fracture in the column the 

 greater is the tendency for the function of respiration 

 to be interfered with. If the lesion be at the upper end 

 of the dorsal spine, then not only will all the 

 abdominal muscles be paralysed, but also all the inter- 

 costals. A fracture, associated with injury to the 

 cord, when above the fourth cervical vertebra, is, as a 

 rule, instantaneously fatal. The phrenic nerve comes 

 off mainly from the fourth cervical nerve, receiving 

 contributions also from the third and fifth. The 

 fourth nerve issues just above the fourth cervical 

 vertebra. If the cord be damaged immediately below 

 this spot, the patient can breathe only by means of 

 the diaphragm, and if the lesion be so high as to 

 destroy the main contribution to the phrenic, respi- 

 ration of any kind becomes impossible. 



Certain disturbances of the act of micturition are 

 frequent in cases of injury to the cord. The reflex 

 centre for this act is lodged in the lumbar enlarge- 

 ment. The irritation of the vesical walls, produced 

 by the increasing distension of the bladder, provides 



H H 



