506 SURGICAL APPLIED ANATOMY. [Cha P . xxiv. 



months of foetal life the medulla spinalis occupies the 

 whole length of the vertebral canal, but after the third 

 month the canal and lumbar and sacral nerves grow 

 so much faster than does the cord itself, that by the 

 time of birth it reaches no farther than the third 

 lumbar vertebra. It is obviously a great advantage, 

 in cases of injury, that the spinal medulla does 

 not occupy that part of the vertebral pillar which joins 

 the base of the column, and which permits not only 

 of considerable movement, but is liable also to frequent 

 wrenches and strains. It is important to recollect 

 that although the cord itself ends at the spot indicated, 

 the dura mater, the arachnoid, and the collection of 

 cerebro-spinal fluid extend as far as the second piece 

 of the sacrum. Injuries inflicted, therefore, upon the 

 spine as low down as this latter point, may cause death 

 by inducing inflammation of the meninges. The cord 

 in the dorsal region measures about 10 mm. from side 

 to side, and 8 mm. in the antero-posterior direction. 

 The cervical enlargement is largest opposite the fifth 

 or sixth cervical vertebrse, where it measures about 

 13 mm. from side to side. The greatest part of the 

 lumbar enlargement is opposite the twelfth dorsal 

 vertebra, where its lateral measurement is about 

 12 mm. 



The spinal dura mater is a strong and substantial 

 membrane, and between it and the walls of the ver- 

 tebral canal a considerable space exists occupied by 

 loose areolar tissue and a plexus of veins. It will be 

 readily understood that injury and inflammation of 

 the meninges, as results of lesions applied to the spine, 

 are much less frequent than are like complications 

 after injuries to the skull. The looseness of the spinal 

 dura mater, its freedom from any but slight and 

 occasional attachments to the bone, and the space 

 around it in which effusions can extend with little 

 possibility of becoming limited, will explain, the rarity 



