THE SPINAL CORD 



they give rise, as sensor, thermal, tactile, etc., so these nerve-cells may be 

 similarly classified according as they transmit their excitations to those 

 specialized areas in the cerebral cortex in which these different sensations 

 arise. 



The emissive cells are efferent or motor in function, inasmuch as the 

 excitation arising in them is transmitted outwardly through their axons to 

 muscles, glands, blood-vessels and viscera, imparting to them motion, 

 either molar or molecular. As the efferent fibers in the ventral roots of 

 the spinal nerves are classified (see page 99) in accordance with their physio- 

 logic action into motor, secretor, vaso-motor, viscero-motor and pilo-motor 

 nerves, so the nerve-cells of which the nerves are integral parts may be 

 classified physiologically as motor, vaso-motor, secretor, viscero-motor and 

 pilo-motor. Collections or groups of such cells are termed "centers." 



The Structure of the White Matter. A transverse section of the cord 

 shows that the white matter completely covers the gray matter except where 



FIG 220. TRANSECTION OF THE CERVICAL SPINAL CORD SHOWING ITS CHIEF SUBDIVISK 



(After Mills.) \^ 



the posterior horns reach the surface. Anteriorly the white matter of each 

 lateral half is connected by a narrow strip or bridge of white matl 

 anterior commissure. Microscopic examination shows that the white 

 is composed of vertically disposed medullated nerve-fibers which are devoid 

 of a neurilemma. These fibers are supported partly by a framework of 

 connective tissue, and partly by neuroglia. The white matter of each 

 of the cord is anatomically divided into an anterior, a lateral, and a post, 

 column by the anterior and posterior roots of the spinal nerves 



