Chap, xxiv.] THE SPINE. 551 



in the spine of those complications which follow upon 

 depressed bone, and extravasations of pus and blood in 

 connection with the dura mater within the skull. The 

 plexus of thin- walled veins that occupies the interval 

 between the theca and the bones may prove a source 

 of extensive haemorrhage in cases of injury to the 

 column. The blood so poured out tends to gravitate 

 to the lowest part of the canal, and when sufficient in 

 quantity may produce pressure effects upon the me- 

 dulla spinalis. 



Over the arches at the posterior aspect of the ver- 

 tebrae is situate a plexus of vessels (the dorsal spinal 

 veins) that receives blood from the muscles and inte- 

 guments of the back. These vessels communicate 

 through the ligamenta subflava with the venous 

 plexuses within the spinal canal, and by means of 

 tins communication inflammation from without may 

 be conducted to the theca of the cord. Thus spinal 

 meningitis has followed upon deep bed-sores, and upon 

 suppurative affections situated in the immediate 

 vicinity of the spinal laminae. 



Within the dura mater are two spaces, the sub- 

 dural and the subarachnoid, as in the skull. They 

 are occupied by a considerable quantity of cerebro- 

 spinal fluid, continuous with the collection within the 

 cranium. By means of this open communication inflam- 

 matory affections may readily spread from the cord to 

 the brain. Into these spaces blood may be extrava- 

 sjited in cases of injury. Instances have been recorded 

 where the theca has been opened by a wound, and the 

 cerebro-spinal fluid has escaped in large quantities. 



The position of the cord is such that it is not 

 readily reached in incised and punctured wounds. The 

 only spots at which it is easy of access are the intervals 

 between the atlas and occiput and the atlas and axis. 

 Many cases have been recorded of fatal wound of the 

 cord in these positions. Lower down in the column 



