434 



THE INTERNAL STRUCTURE 



stance of the 'perns Varolii ' (fig. 154), the sites in which 

 decussation of motor channels takes place, are altogether 



limited in area when com- 

 pared with what ohtains for 

 sensory channels. 



The longitudinal fihres of 

 the Spinal Cord are in the 

 main divisible (if we exclude 

 those specially in relation 

 with the Cerebellum) into 

 three categories, viz., (1) 

 fibres transmitting 'ingoing ' 

 currents towards the Brain ; 



(2) fibres which transmit 

 ' outgoing ' currents ; and 



(3) fibres of a ' commissural ' 

 order, serving to connect 

 separate groups of cells or 

 centres in different parts of 

 the Spinal Cord itself, or in 

 the Spinal Cord and Me- 

 dulla. 



The Spinal Cord being, 



fc 



B 



FIG. 154. Diagram illustrating the 

 place and , mode of ' decussation ' of 

 Motor Fibres in the Medulla and in the 



pons. (Broadbent.) B, B, two sets of moreover, a bilaterally sym- 



nuclei of brachial plexus, not con- metrical Organ, the gl'OUpS 

 nected by transverse commissures ; _ 



o, o', two sets of ocuio- motor nuclei in oi cells above referred to 



Pons, freely connected with one another are s i m jl ar ly represented in 



by transverse commissural fibres. l i 



8,8', motor fibres from Corpus Striatum. each half of it (fig. 19) ; and 



the similar Motor and Sen- 

 sory regions of these two halves of the Cord and Medulla 

 are to a considerable extent brought into structural relation 

 with one another by means of numerous transverse ' com- 

 missural ' fibres. 



The first two sets of longitudinal fibres, above referrec 



