SPINAL CORD. 



159 



proportion of white to gray matter is greater than else- 

 where ; and as the cord approaches the medulla oblongata 

 its central gray mass becomes irregular in form and begins 

 to break up into smaller portions. If lines be drawn on 

 the transverse section of the cord from the tip of each horn 

 of the gray matter to the nearest point of the surface, the 

 white substance in each half will be divided into three por- 



FIG. 64. The spinal cord and nerve-roots. A, a small portion of the cord 

 seen from the ventral side ; B. the same seen laterally ; C, a cross-section of the 

 cord ; 7), the two roots of a spinal nerve ; 1. anterior (ventral) fissure ; 2, poste- 

 rior (dorsal) fissure ; 3, surface groove along the line of attachment of the ante- 

 rior nerve-roots : 4, line of origin of the posterior roots; 5, anterior root fila- 

 ments of a spinal nerve ; 6. posterior root filaments ; 6'. ganglion of the poste- 

 rior root ; 7, 7', the first two divisions of the nerve-trunk after its formation by 

 the union of the two roots. 



tions: one between the anterior fissure and the anterior 

 cornu, and called the anterior white column ; one between 

 the posterior fissure and the posterior cornu, and called the 

 posterior white column; ^rhile the remaining one lying in 

 the hollow of the crescent and between the two horns is the 

 lateral column. In addition to this a certain amount of 

 white substance crosses the middle line at the bottom of 



