TEANSVEESE TEANSMISSION. 299 



a considerable degree, accomplished through the vesicular substance, the 

 quality of which, in this respect, has been explained in the preceding 

 chapter. But, besides this, the exterior fibrous structures possess a like 

 function, correspondingly as they are connected with the motor or sen- 

 sory roots of the nerves, the anterior columns being motor, and the pos- 

 terior apparently sensory. 



The spinal cord not only permits the passage of influences in its longi- 

 tudinal, tut also in its transverse direction. This is what Transverse 

 might be anticipated from the structure and functions of the transmission of 

 cells of its gray interior. If the cord be cut half through in u 

 a given place, and again be cut half through on the opposite side, at a 

 little distance above or below, impressions may be conducted through 

 the intermediate portion, the vesicular material being then their only 

 channel. 



In a memoir on the distribution of the fibres of the sensitive roots, and 

 on the transmission of impressions in the spinal cord, Dr. Brown . Se uard 

 Brown-Sequard, referring to the two theories entertained at on the conduc- 

 present 1st. That sensitive impressions reaching the cord tlonofthecord - 

 pass in totality to the brain along the posterior columns ; 2d. That such 

 impressions so arriving pass directly to the central gray substance, which 

 transmits them upward offers reasons for supposing that both these 

 theories, and especially the first, are contradicted by facts. 



It is his opinion that sensitive impressions reaching the cord pass in 

 different directions, some ascending, others descending, but both going in 

 part by the posterior columns, and in part by the posterior gray horns, 

 and perhaps by the lateral columns, to penetrate, after a short distance, 

 the gray central substance by which, or in which, they are transmitted 

 to the brain. 



He also shows that sensitive impressions of one lateral half of the 

 body are transmitted principally in a crossed manner, that is to say, that 

 they follow more particularly the opposite half of the cord to reach the 

 brain ; that the decussation of the conducting elements for sensitive im- 

 pressions is not made, as is commonly said, at the anterior extremity of 

 the pons ; that the gray substance does not possess the property of 

 transmitting sensitive impressions in every direction, as some have sup- 

 posed ; that most, if not all the conducting elements for sensitive im- 

 pressions decussate in the spinal cord, the decussation occurring in part 

 almost immediately on their entry into the cord, but that a few make 

 their decussation at a certain distance above the point of entry, the ma- 

 jority, however, descending in the cord, and making their decussation 

 below the point of entry ; that if there are conducting elements for sen- 

 sitive impressions which ascend throughout the entire length of the cord 

 to make their decussation in the brain, their number must be very small ; 



