IE SPINAL MARROW AND ITS FUNCTIONS. 137 



ter, like the brain ; the situation of the two is, however, 

 reversed ; the medullary matter being disposed in a thin 

 layer upon the surface, while the grey portions occupies the 

 centre. We, however, find the same arrangement in the 

 medulla oblongata, and the central parts of the cerebrum 

 and cerebellum. The chord, as t have already mention, 

 ed, is divided into two lateral halves by a groove in front 

 and a similar groove behind. Besides this, there are on 

 each side two lateral grooves faintly marked, from which 

 the anterior and posterior nerves have their origin, so that 

 in fact, the cord consists of four columns ; from the two 

 anterior of which, the nerves ofjnotion spring, and from the 

 two posterior those of sensation.^ 



a, Spinal marrow. 

 6, Fibres of sensation. 

 c, Fibres of motion. 

 e, Nerve. 



6. There are thirty pairs of nerves that spring from the 

 spinal marrow, viz., eight from the region of the neck, twelve 

 from that of the back, and five from the pelvis. By examin- 

 ing the above cut, it will be seen that they arise by two 

 roots, one from the anterior, and one from the posterior 

 column. The fibres of the posterior swell out into a gang- 

 lion before they unite with the anterior. 

 12* 



