700 STRUCTURE OF THE CEREBRUM [CH. XLVTII. 



motor area (the convolutions immediately in front of the Eolandic 

 fissure). The axon of each of these giant pyramids originates from 

 its base, and fig. 438 (next page) shows in outline the destination 

 of the fibres. 



1 is a cell of the motor or Eolandic area of the cerebral cortex ; 

 its axon (Ax) passes down in the pyramidal tract, and crosses the 

 middle line (oo) at the pyramidal decussation. It gives off collaterals, 

 one of which (assoc.) is an association fibre passing to terminate in 

 the cortex of a neighbouring convolution ; another, labelled commis, is 

 a commissural fibre passing in the corpus callosum to the opposite 

 hemisphere ; others pass into basal ganglia. 



In the cord, collaterals pass off to end in synapses around cells 

 at the base of the posterior horn, and the main fibre has a similar 

 termination; from each of these posterior horn cells, a short axon 

 passes to end in an arborisation around an anterior cornual cell; 

 only one of these is shown ; the motor nerve-fibre passes from this 

 to muscular fibres, to terminate in end-plates there. 



The pyramidal cell numbered 2 is taken to illustrate the similar 

 relationships between the cortex and muscles supplied by cranial 

 nerves ; its axon is represented as ending in the motor nucleus of 

 the seventh nerve, and the new axon arising there passes to face- 

 muscles. In order to prevent confusion in the diagram, cell 2 is 

 placed in one of the upper convolutions ; the face area of the cortex 

 is really below those for the limbs. 



The cell numbered 3 illustrates the fact that certain axons never 

 reach the spinal cord, but terminate in the grey matter of the mid- 

 brain and pons ; such fibres may therefore be called cortico-pontine, 

 in contradistinction to the pyramidal fibres, which are cortico-spinal. 

 From these subsidiary masses of grey matter in the pons and mid- 

 brain, new tracts, such as the bundle of Monakow or prepyramidal 

 tract, arise (ponto-spinal fibres), which continue on the impulse to the 

 anterior cornual cells. 



No attempt has been made in this diagram to insert autonomic 

 fibres with their accessory cell-stations in ganglia outside the 

 central nervous systems. For these the reader is referred back to 

 Chap. XVII. 



The afferent projection system. This is also indicated in outline 

 in the same diagram (fig. 438). A is a cell of one of the spinal 

 ganglia on the posterior nerve-roots; its peripheral axon terminates 

 in muscular tendons or in skin, and the impulse it conducts is 

 afferent, as shown by the arrow. The central axon passes into 

 the spinal cord, and its impulse ultimately arrives at the cortex of 

 the opposite side through several intermediate cell-stations. The 

 last relay on the sensory path passes from O.T., the optic thalamus, 

 to the cortex, and is linked up to the motor cell (1) by the associa- 



