STRUCTURE OF THE CEREBRUM. [OH. XLVI. 



claustrum in the region of the Island of Reil has been already 

 alluded to (p. 645). 



By Golgi's method the arrangement of these cells has been re- 

 cently made out much better. The diagram on p. 648 (fig. 48 1) is 

 taken from Ramon y Cajal's Croonian Lecture, and the following 

 two (figs. 482 and 483) are from photo-micrographs kindly lent 

 me by Dr. Mott. Fig. 482 represents a section through the motor 

 cortex of the human brain, and shows very beautifully the large 

 pyramidal cells with dendrons passing off from their corners, and 

 the axis-cylinder process passing from the base of each towards 

 the white matter, giving off collaterals on the way. Neuroglia- 

 cells are also seen. 



Fig. 483 is a high-power view of the same; in the lower part 

 of the diagram some of the neuroglia-cells are seen in the sheath 

 of a small blood-vessel. 



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, ( i ) 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 tract. These are called Projection 

 fibres. As they pass down they give off collaterals to the ad- 

 jacent 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 anterior horn of the 

 opposite side of the spinal cord. 



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. 



We are now in a position to complete diagram 453 (p. 61 1), and 

 obtain an idea of the relations of the principal cells and fibres of 

 the cerebro-spinal nervous system to one another. 



Pyr. (fig. 484) is a cell of the Rolandic area of the cerebral cortex ; AX is its 

 axis-cylinder process which passes down in the pyramidal tract, and crosses 

 the middle line AB at the pyramidal decussation. It gives off collaterals, one 

 of which (call} is shown passing in the corpus callosum to terminate in an 

 arborisation in the cortex of the opposite hemisphere ; another (str) passes 

 into the corpus striatum. In the cord collaterals pass off and end in arbori- 



