118 



' Me&oll 



Decussatio 







"ci\ 

 Fibrae decuss. 





Pyramides Pymmides 



(D 



402. Transverse Sections of the Medulla Oblongata 



and Spinal Cord. After Fr. Arnold. 



The spinal cord is not uniformly cylindrical, but marked by 

 two enlargements, an upper or cervical, and a lower or lumbar, corres- 

 ponding to the points of exit of the largest nerves. It is divided into two 

 symmetrical halves, each of which consists of an external white cortex, and 

 an internal grey nucleus ; the fissures which so divide it, are on the 

 anterior surface, along the middle line, the anterior median f i s s u r e, 

 Sulcus longitudinalis anterior, and on the posterior surface, the posterior 

 median fissure, Sulcus longitudinalis posterior ; the anterior median fissure 

 is marked along the whole length of the cord, the posterior, well marked 

 only at the cervical portion and Conus terminal is. 



The two parts of the central grey nucleus are united by the middle 

 grey commissure, in front of it the two halves of the external white 

 substance by the anterior white commissure; between these two 

 commissures the small central canal of the spinal cord extends 

 through the whole length of the cord. The relation of the grey nucleus to 

 the white cortex varies in different situations ; the shape of the former 

 corresponds in general to an x with narrower posterior cornua 

 and broader anterior cornua; the white matter increases in quantity 

 from below upwards. The grey nucleus consists principally of multi- 

 polar ganglion cells; the white matter chiefly of longitudinal nerve 

 fibres, with the transverse fibres of the roots of the spinal nerves. 



The longitudinal fibres form six columns, separated by shallow 

 fissures ; they are : 



T w o anterior c o 1 u m n s, on both sides of the anterior median fissure ; 



Two lateral coin m n s, between the origins of the anterior and 

 posterior roots of the spinal nerves ; 



Two posterior columns, on both sides of the posterior median 

 fissure ; 



Opposite the uppermost cervical vertebrae, the pyramidal columns, 

 which take part in the decussation, are found between the anterior 

 columns; between the posterior columns are found the Funiculi graciles, which 

 form with the c u n e a t e f u n i c u 1 i the r e s t i f o r m bodies. 



