PROPERTIES OF THE SPINAL CORD. 121 



The Sensory fibres, which convey the impression made upon the peri- 

 phery to the cord and brain, pass into the cord through the posterior roots 

 of spinal nerves; they then diverge and enter the gray matter at different 

 levels, and at once decussate, passing to the opposite side of the gray 

 matter. The sensory tract passes upward, through the cord, the medulla, 

 pons Varolii, the superior portion of the crura cerebri, the posterior third 

 of the internal capsule, to the sensory perceptive centre, located in the 

 hippocampus major and unciate convolution (Ferrier). Through this decus- 

 sation each half of the brain governs the sensibility of the opposite half 

 of the body. 



Properties of the Spinal Cord. Irritation applied directly to the 

 antero-lateral white columns produces muscular movements but no pain ; 

 they are, therefore, excitable but insensible. 



The surface of the posterior columns is very sensitive to direct irritation, 

 especially near the origin of the posterior roots ; less so toward the posterior 

 median fissure. The sensibility is due, however, not to its own proper 

 fibres, but to the fibres of the posterior root which traverse it. 



Division of the antero-lateral columns abolishes all power of voluntary 

 movement in the lower extremities. 



Division of i\\e posterior columns impairs the power of muscular coordi- 

 nation, such as is witnessed in locomotor ataxia. 



The gray matter is probably both insensible and inexcitable under the 

 influence of direct stimulation. 



A transverse section of one lateral half of the cord produces : 



(1) On the same side, paralysis of voluntary motion and a relative or 

 absolute elevation of temperature and an increased flow of blood in the 

 paralyzed parts ; hypersesthesia for the sense of contact, tickling, pain and 

 temperature. 



(2) On the opposite side, complete anaesthesia as regards contact, and 

 tickling and temperature, in the part's corresponding to those which are 

 paralyzed in the opposite side. Complete preservation of voluntary power 

 and of the muscular sense. 



A vertical section through the middle of the gray matter results in the 

 loss of sensation on both sides of the body below the section, but no loss of 

 voluntary power. 



