HISTOLOGY. 77 



each half into three columns, we have the anterior, 

 posterior and lateral columns of each half, making 

 six columns in the cord. In the lower cervical and up- 

 per thoracic region two more divisions appear in the 

 posterior column, the column of Goll (placed near the 

 posterior fissure) and the column of Burdoch. The 

 white matter is connective tissue and nerve fibers, hav- 

 ing a large number of glia cells interspersed in them. 

 The nerve fibers have a medullary sheath, but no neit- 

 rilemma. "The nerve fibers run in the same direction 

 as the long axis of the spinal cord ; a few may be seen 

 which run across the cord." Leroy. Around the en- 

 tire cord are found three protecting membranes: the 

 dura mater, arachnoid and pia mater. The space be- 

 tween the dura mater and arachnoid is called the sub- 

 dural space. The space between the arachnoid and 

 pia mater is called the sub-arachnoidaj space. All 

 these membranes are composed of white fibrous tissue 

 and endothelial cells. They are all more or less con- 

 nected by fine fibers of fibrous tissue, which run trans- 

 versely to the long axis of the cord. The Pacchion- 

 ian bodies are large papillae projecting upward into the 

 subdural space. The blood vessels are found in the 

 dura mater and pia mater; but none are found in the 

 arachnoid. They are most numerous in the pia mater. 

 The gray matter of the cord is arranged in the shape 

 of the letter H. The long arms of the H are directed 



