230 CLINICAL APPLIED ANATOMY. 



which ascend from the lowest parts of the cord are longest and 

 travel further from their trophic centres in the posterior root 

 ganglion, hence they may be more susceptible to pressure. 

 Secondly, as the fibres of the successive sensory roots enter the 

 cord, those of them which ascend in the posterior columns tend 

 to displace inwards the fibres which enter immediately below 

 the'm, so that the fibres which enter lowest finally come to lie 

 near the surface of the postero-median column close to the 

 median septum, whilst the higher fibres approach nearer and 

 nearer the central part of the cord. Consequently fibres from 

 the lowest roots in the posterior columns at all events, are most 

 exposed to concentric compression. But it is stated that the 

 march of anaesthesia may be the same in eccentric pressure, such 

 as occurs for instance with haemorrhage into the grey matter. 



The motor paralysis below the level of the lesion is of the 

 spastic type, and accompanied by interference with the action of 

 the bladder and rectum. Pressure on the pyramidal tracts 

 accounts for the motor symptoms. Curiously enough the direction 

 of invasion of paralysis is the reverse of the anaesthesia, the 

 highest muscles suffering first. No arrangement of fibres in the 

 pyramidal tracts is at present known which would account for 

 this method of invasion. The conversion of the spastic into a 

 flaccid condition in the terminal stages of the disease is held to 

 indicate the establishment of a total transverse lesion of the cord, 

 possibly induced by softening or myelitis. 



There are certain motor symptoms in compression paraplegia 

 which are special to definite regions of the cord. These comprise 

 alterations in respiration, alterations in the pupils, alterations in 

 the heart's action, vaso-motor and secretory phenomena. 



Since the main motor supply of the diaphragm is derived from 

 the fourth cervical nerve, fibres of which together with some 

 from the third and fifth nerves make up the phrenic trunk, a 

 lesion in this region is peculiarly dangerous. It not only cuts off 

 the impulses descending to the intercostals from the respiratory 

 centre, but also gives rise to paralysis of the diaphragm so that 

 respiration ceases. 



