Spinal Cord 213 



to end in the surrounding spinal veins. The spinal veins empty into 

 the vertebral, intercostal lumbar, and lateral sacral veins. Hcemorrhage 

 from these veins, perhaps the result of injury, causes pressure upon the 

 cord and sudden paraplegia. Suspension in the treatment of diseases 

 of the spinal cord may possibly owe its value to the stimulus which is 

 thereby imparted to the circulation in the veins of the cord (p. 214) 

 and of the canal. 



TOY fracture through sacro-coccygeal joint, v. p. 362. 



THE SPINAL CORD 



The spinal cord is the continuation of the encephalon towards the 

 trunk and extremities. It begins at the lower border of the medulla 

 oblongata, at the level of the first cervical vertebra, and extends to the 

 first lumbar, where it breaks up into the cauda equina. In early foetal 

 life it reaches to the very end of the spinal canal, but its subsequent 

 growth does not keep pace with that of the canal. Its average length 

 in the adult is i| ft. and its weight i oz. 



It has two enlargements, one in the lowest cervical region, the other 

 in the lowest dorsal. From the cervical enlargement the nerves issue 

 for the brachial plexus, and from the lumbar enlargement emerge the 

 nerves for the lumbar and sacral plexuses. The cord is enclosed in 

 the pia mater, arachnoid, and dura mater, but even with these invest- 

 ments it does not nearly fill the canal, being separated from the bony 

 wall by a plexus of veins and by loose connective tissue. Partly to this 

 fact, and partly to its being suspended in cerebro-spinal fluid, does the 

 cord owe its comparative freedom from injury. 



The dura mater is continuous with that lining the cranium, but it 

 does not act as periosteum, nor does it enclose venous channels. It is 

 firmly attached to the border of the foramen magnum and to the back 

 of the body of the axis. It forms a sheath to the cauda equina as far 

 as the top of the sacrum, and gives an investment to each nerve as it 

 passes out. 



The arachnoid (apaxvrj, <>$, ' fine as a spider's web ') intervenes 

 between the dura and pia mater, being continuous with that of the 

 brain. External to it is the sub-dural space, containing some cerebro- 

 spinal fluid, and between it and the pia mater is the sub-arachnoidean 

 space, the fluid of which is abundant, and which communicates with 

 that in the cerebral ventricles through an opening in the floor of the 

 fourth ventricle. In the case of a large spina bifida (p. 204) a distinct 

 wave of fluctuation may sometimes be obtained by compressing the 

 tumour with one hand whilst the other hand is over the anterior fonta- 

 nelle ; if, however, the pressure be made roughly, cerebral irritation 

 results. 



The fluid of the spinal canal, be it clearly understood, is in the 



