COMPEESSION OF THE SPINAL COED. 229 



of the extremities, but recognition is not so easy when the inter - 

 costals or muscles of the abdomen are involved. It is possible, 

 however, to tell if there is any weakness of the upper or lower 

 parts of the recti by observing the movement of the umbilicus. 

 This normally does not vary its position on the patient sitting 

 up, but if the part of the muscle below the umbilicus is paralysed 

 the unopposed action of the upper part will draw up the umbilicus. 

 If the part of the rectus above the umbilicus is affected, the 

 umbilicus will be drawn downwards instead of upwards. The 

 rectus is supplied by the fifth to the twelfth dorsal nerves. As 

 the umbilicus is in the field of the ninth dorsal root, a lesion 

 paralysing that part of the rectus which lies below it belongs to 

 the tenth, eleventh or twelfth dorsal segments. 



In addition to the radiating pains produced by compression of 

 the spinal roots, the local pressure on the dura mater is respon- 

 sible for a deep-seated local pain. This is probably explained by 

 the fact that the dura is supplied with nerve filaments, and is 

 known to be extremely sensitive. 



Besides root symptoms, compression produces symptoms refer- 

 able to the cord itself. The points at which there is the least 

 spare space in the theca are said to lie in the mid-cervical region 

 and at the two extremities of the dorsal region, and these are the 

 situations in which most instances of compression by tumour 

 occur. The pressure exerted on the cord is at first more or less 

 localised, and so unilateral symptoms may be produced, becoming 

 bilateral as the pressure increases. The compression may 

 produce local softening, either from occlusion of vessels or the 

 onset of an inflammatory condition. 



The compression symptoms usually, but not invariably, occur 

 in the following order : Pain, motor paralysis, sensory paralysis. 

 The pain, which is distinct from the root pains and localised 

 pain already mentioned, is often referred to points at some 

 distance below the lesion in the spinal cord, not infrequently 

 to joints. Also when anaesthesia develops the sensation is first 

 affected in the lower parts of the body. There are two anatomical 

 facts which may have some bearing on this. First, the fibres 



