ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 613 



white substance which surrounds the anterior cornua reaches from 

 the anterior median groove to the posterior cornua. It seems to 

 form a homogeneous column: the antero-lateral column. 



In the rear, on the contrary, the posterior cornua sharply sepa- 

 rate the preceding to form posterior columns. They lie between the 

 posterior median groove and the posterior cornua. In the cervical 

 region the posterior column is sharply divided into two secondary 

 columns by the posterior intermediate groove. These are the 

 columns of Goll (next to the posterior median groove) and Burdach 

 (in apposition with the posterior cornu). 



From measurements by Stilling it seems that the 'cervical swell- 

 ing results from a localization of superdevelopment of both gray and 

 white matter of the cord. The lumbar enlargement Js almost exclu- 

 sively formed by a localized superdevelopment of gray substance. 

 This is readily explained by the constitution of the columns them- 

 selves. Excepting the fibers forming the roots of the spinal nerves, 

 the columns of white matter are formed of descending, or motor, and 

 ascending, or sensory, fibers. The motor bundle successively gives off 

 fibers to the motor roots of the spinal nerves to such a degree that 

 in their descent their volume proportionately diminishes. 



The sensory, or ascending, bundle, receiving fibers from each 

 posterior root which comes from a sensory nerve, enlarges as it 

 ascends. Hence it results that at the level of the lumbar enlarge- 

 ment the bundles are at a minimum, the ascending bundle just com- 

 mencing, while the descending bundle is nearly spent. 



Minute Constitution of the Cord. The spinal cord is composed 

 of fibers, nerve-cells, neuroglia, and blood-vessels. In the white sub- 

 stance there are found only nerve-fibers and neuroglia; in the gray 

 .bstance, nerve-cells and fibers plunged in a stroma of neuroglia. 



WHITE SUBSTANCE. The white matter is composed principally 

 of medullated fibers without the sheath of Schwann. The fibers in 

 the white substance are, for the most part, arranged longitudinally; 

 those which pass to the nerve-roots, as well as those fibers which pro- 

 from the gray matter into the columns, possess an oblique 

 iurse. In addition there are decussating fibers in the white com- 

 missure. 



(On cross-section the fibers (which are of different sizes) present 

 appearance of small circles with a rounded dark spot in their 

 ters. This latter represents the axib cylinder of the fiber. 

 The diameter of the fibers varies from 1 / fl000 to 1 / 1200 inch. 

 e most voluminous are the motor parts of the antero-lateral 



mum 



ceed 

 cours 



