Chap, xxiv.] THE SPINE. 509 



its bony canal, and is separated from the walls of that 

 canal on all sides by a considerable interval. It is, 

 indeed, only held in position by the nerve trunks that 

 pass out from it through the intervertebral foramina, 

 and by its connections with the theca. Above, it is 

 connected with that part of the brain that lies upon 

 the largest intracranial collection of the cerebro-spinal 

 fluid (page 27), and it would appear that the most 

 violent movements possible of the brain within the 

 skull could be but very feebly communicated to the 

 spinal cord. The cord, moreover, within its theca, is 

 surrounded on all sides by a space occupied by cerebro- 

 spinal fluid. It is difficult to understand, therefore, 

 how a structure so protected can be so violently dis- 

 turbed by a shock received upon the body as to undergo 

 a grave and progressive loss of function. The cord is, 

 indeed, somewhat in the position of a caterpillar sus- 

 pended by a thread in a phial of water. It would 

 probably be difficult to permanently disturb the in- 

 ternal economy of such an insect (even if it had a 

 structure as elaborate as the cord) by other than vio- 

 lence that would be comparatively excessive. 



Contusion and crushing: of the cord. As 

 has been already observed, the gravity of fractures and 

 dislocations of the spine depends upon the extent of 

 the damage received by the cord. In these accidents 

 it is very usual for some part of the injured vertebrae 

 to be projected into the spinal canal, so as to press 

 upon or actually crush the delicate nerve centre that 

 it contains. 



It is needless to observe that the cord is extremely 

 soft, and thus it happens that it may be entirely broken 

 up by violence without the membranes being percep- 

 tibly damaged. Indeed, in fracture-dislocations it is 

 unusual for the theca to be torn, and it is possible for 

 the cord to be quite crushed at some one spot without 

 the corresponding pia mater being in any way lacerated. 



