304 NEUROLOGY, OR ANATOMY OF NERVOUS SYSTEM 



into the posterior median fissure. It ensheathes the spinal 

 nerves, and ends below in the filum terminate, which joins the 

 dura at the upper limit of the sacral canal. 



Along the anterior median surface of the pia runs a prominent 

 fibrous band, the lined splendens, and between the two nerve 

 roots on each side is a serrated band, the lig amentum dcnticu- 

 latum, the points of the serrations, about twenty on each side, 

 being attached to the dura between the pairs of nerve roots. 



The spinal cord is about 18 to 20 inches long, weighs about 

 an ounce, and occupies about the upper two-thirds of the spinal 

 canal, viz., from the foramen magnum to the lower border 

 of the first lumbar vertebra. It ends in a narrow cord of gray 

 substance which runs in the midst of the filum terminale. 



The enlargements of the spinal cord are two an upper or 

 cervical, extending from the third cervical to the first or second 

 thoracic vertebra, and a lower or lumbar, from the tenth thoracic 

 to about the first lumbar. These enlargements correspond 

 to the origin of the nerves which supply the upper and lower 

 extremities respectively. The surface of the cord presents 

 several fissures, which will now be described. 



The fissures of the spinal cord are an anterior and a posterior 

 median, and laterally on each side are several grooves called 

 fissures. 



The anterior median fissure extends through about one- 

 third the thickness of the cord, as far as the anterior white 

 commissure, and contains a fold of the pia. 



The posterior median fissure extends about halfway through 

 its substance to reach the posterior or gray commissure. It 

 is not a real fissure, being filled up by connective tissue. 



The anterolateral fissure is merely the line of origin of the 

 anterior nerve roots, while the posterolateral is in reality a 

 groove, and runs along the line of origin of the posterior nerve 

 roots. 



Lastly, a slight groove, the posterior paramedian fissure, 

 marks off the posterior intermediate column on either side of 

 the posterior median fissure. 



The columns of the spinal cord are divisions made by these 

 fissures, three on each side. 



The anterolateral column, between the anterior median and 

 posterolateral fissures. The posterior column, between the 

 posterolateral and posterior median fissures, becomes divided, 



