530 THE THORAX AND VERTEBRAL COLUMN 



viscera is lost and reflex evacuations occur. If the injury occurs 

 at or below the level of these centres, the viscera are paralysed 

 and there is, at first, retention of urine, and, later, a continual 

 overflow. In many cases, however, these centres are only 

 partially affected. 



A complete hemi-lesion of the spinal medulla causes complete 

 paralysis of the muscles of the same side of the body which are 

 innervated by the segments below the lesion. Sensory changes 

 also occur, but, as all the fibres which convey painful and thermal 

 sensations and most of those which convey tactile sensations 

 cross the middle line shortly after they enter the spinal medulla, 

 these changes are only found on the opposite side of the body. 

 Muscle sense and joint sense, however, are conveyed by fibres 

 which ascend on the same side till they reach the medulla 

 oblongata, where they decussate. Loss of muscle and joint 

 sense, therefore, is restricted to the paralysed limb. A narrow 

 zone of anaesthesia is present at the upper limit of the motor 

 paralysis. In this situation the sensory fibres are involved as 

 they enter the spinal medulla and the position of the anaesthetic 

 strip is a certain indication of the site of the lesion. Immediately 

 above the zone of anaesthesia there is usually a narrow zone of 

 hyperaesthesia. 



Complete destruction of the spinal medulla at the level of the 

 fifth cervical segment is consistent with life, since the nerve- 

 supply to the diaphragm (phrenic nerve, C. 3, 4, and 5) is not 

 at once destroyed. This lesion is accompanied by total paralysis, 

 of the upper neurone type, of the trunk and all the limbs. The 

 sensory paralysis does not extend so high on the anterior surface 

 as it does on the posterior surface of the body. Anteriorly, the 

 line of anesthesia corresponds to the second costal cartilage, as 

 the skin above that level is supplied by C. 3 and 4 (Fig. 72). 

 Posteriorly, the line lies at a higher level, since the posterior 

 rami of the third and fourth cervical nerves do not extend so 

 far downwards as their anterior rami (Fig. 3). This condition 

 is usually followed by an ascending myelitis, which destroys 

 the spinal centres of the phrenic nerve, causing death in a few 

 days. 



When the sixth cervical segment is destroyed, the muscles 

 supplied by C. 5, being unopposed, produce a characteristic 

 attitude. The upper limbs are abducted and laterally rotated 

 at the shoulder, the forearm is flexed and supinated. An 

 ascending myelitis usually occurs, and destruction of the fifth 



