CH. XLVI.] THE CEREBRAL CORTEX 659 



line of Gennari in the occipital region. There can be little or no doubt 

 that these are association tracts finking the convolutions together. 



The cells of the cortex thus give rise to the motor or efferent 

 fibres ; these pass into the white matter of the interior of the brain. 

 Some go either directly or by collaterals, (1) to the cortex of more 

 or less distant convolutions. These are called Association fibres. (2) 

 Others pass to the corpus callosum, and so reach the cortex of the 

 opposite hemisphere. These are called Commissural fibres. In each 

 case they terminate by arborisations (synapses) around the cells of 

 the grey matter of the cortex ; while others again, especially those 

 of the largest pyramidal cells, extend downward through the corona 

 radiata and internal capsule, and become, (3) fibres of the pyramidal 



FIG. 481. Human cerebral cortex : Golgi's method. High power. (Mott.) 



tract. These are called Projection fibres. As they pass down they 

 give off collaterals to the adjacent grey matter, to the opposite 

 hemisphere vid the corpus callosum, to the corpus striatum and the 

 optic thalamus, which terminate there by arborisations; the main 

 fibres terminate in synapses round the multipolar cells of the grey 

 matter of the opposite side of the spinal cord. These are termed the 

 cortico -spinal fibres ; von Monakow has shown that some of the 

 pyramidal fibres terminate in the mid-brain and pons (cortico-pontine 

 fibres), and a fresh relay of fibres thence continues the impulse 

 downwards. 



The cells of the cortex are, in addition to all this, surrounded by 

 the arborising terminations of the sensory nerve-fibres, which, after 

 relays at various cell-stations, ultimately reach the cortex. 



