332 MEMBRANES OF THE SPINAL CORD. 



eral parts of the gray substance, including the tips of the columnar 

 Those branches to the columnar accompany the root-fibers. 



Veins. The veins that carry the blood from the interior of 

 the cord, the venae spinales internae, are the fissural veins, which 

 issue from the fissures, the root-veins, which accompany the ante- 

 rior and posterior root-fibers to the surface of the cord, and a 

 small number of veins that issue from other parts of the surface 

 of the spinal cord. All unite in forming the external spinal plexus 

 (venae spinalis externae) spread over the entire surface of the 

 cord beneath the arachnoid membrane. According to Cunning- 

 ham, the plexus includes six longitudinal veins anterior and 

 posterior median and, on either side, an antero-lateral and a 

 postero-lateral vein placed just behind the respective nerve roots. 

 In the upper cervical region, the plexus forms two or three small 

 veins which empty into the vertebral or inferior cerebellar veins; 

 elsewhere, by a branch along each spinal nerve, the plexus com- 

 municates with the internal vertebral plexus (plexus venosi 

 vertebrales intern!) outside the dura mater, and is drained into 

 the vertebral, intercostal, lumbar and sacral veins. No valves 

 are found in the spinal veins. 



Lymphatics. Perivascular and perineural spaces carry the 

 lymph from the spinal cord. There are no lymphatic vessels 

 in the cord. 



