558 WILL AND 



mental than has been above indicated. The reasons for 

 this opinion must be set forth in detaiL 



The Mechanisms for Primary Automatic Movements, 

 and their Modes of Origin. 



The nervous connections representative of a certain number of 

 Movements which have been commonly performed by the present 

 and many past generations of any race of animals exist in an 

 organized condition in the Spinal Cord and Medulla of such animals. 

 They are represented by the development of certain cell-and-fibre 

 connections in the anterior, or what are known as the ' motor * 

 regions of the Grey Matter of these parts — such mechanisms being 

 in continuity in front with the roots of ' outgoing' nerves, and in 

 relation behind with groups of smaller nerve cells with which the 

 'ingoing ' nerves of the posterior roots are, in their turn, in some sort 

 of structural relation. It is along these latter channels that the 

 sensory Impressions prompting to the Movements of which we 

 have been speaking reach the Spinal Cord or Medulla * 



Many of the corresponding groups of ' motor ' Cells, situated at 

 the same level in the right and left halves of the Cord and Medulla, 

 are intimately connected by transverse * commissural ' fibres— in 

 fact, wherever joint action of the nerve units on the two sides is 

 a matter of common occurrence (fig. 154, o o'). 



Many of the groups of motor cells, at different levels of the 

 cord are also connected with one another into single or multiple com- 

 binations, by longritudinal 'commissural' fibres whose length varies 

 according to the distance apart of the cell groups thus united for 

 conjoint activity. These longitudinal connecting fibres of different 

 lengths, as they pass from cell- group to cell-group, have been 

 ascertained (on the basis of clinico-pathological evidence supplied 

 by persons suffering from spinal disease) to traverse, in part at 

 least, the 'posterior columns' of the Cord. 



Bilateral groups of these cells, existing at various levels in the 

 two ' anterior cornua,' though differing much from one another in 

 the number of the units involved and in the width of the area over 

 which they are distributed, are conceived to be the Spinal and 

 Medullary Nervous Mechanisms needful for the execution of avast 

 multitude of Reflex, or Primary Automatic Movements, also of all 



* See pp. 26, 52. 



