GREY AND WHITE MATTER IN THE SPINAL CORD 863 



matter, known as the corpus dentatum, which is buried in its white 

 core, are also connected by strands of fibres with the central stem and 

 the cerebral mantle. The restiform body or inferior peduncle brings 

 the cerebellum into communication with the spinal cord. The superior 

 peduncle by one path, and the middle peduncle by another, connect it 

 with the cerebral cortex. A great transverse commissure, the corpus 

 callosum, unites the cerebral hemispheres across the middle line, while 

 transverse fibres, that break through the middle lobe or worm, form 

 a similar though far less massive junction between the two hemispheres 

 of the cerebellum. 



The fibres of the nervous system may be divided into (i) fibres 

 connecting the peripheral organs with nerve-cells in the central grey 

 axis; (2) fibres connecting nerve-cells in this central axis with cells 

 in the external or cortical grey tube; and (3) fibres linking cortex 

 with cortex, or central ganglia with each other. In the third group 

 are included (a) fibres which connect portions of the cortex on the 

 same side (association fibres) ; (b) fibres which connect portions on 

 opposite sides of the middle line (commissural fibres) ; (c) fibres which 

 connect the central grey matter at different levels e.g., the proprio- 

 spinal or endogenous fibres of the cord. Our first task is, therefore, 

 to trace the peripheral nerves to their cells of origin or centres of 

 reception* in the nervous stem. And although there is reason to 

 believe that the whole of the peripheral nerves, cerebral and spinal 

 (with the exception of the olfactory and optic, which are rather 

 portions of the brain than true peripheral nerves), form a morpho- 

 logical series, it will be well to begin with the spinal nerves, since 

 their motor and sensory fibres are gathered into different and definite 

 roots, whose course within the cord is, in general, more easily traced 

 than the course of the cerebral root-bundles within the brain. 



SECTION III. ARRANGEMENT OF THE GREY AND WHITE MATTER 

 IN THE SPINAL CORD. 



The grey matter of the spinal cord is arranged on each side in a 

 great unbroken column of roughly crescentic section, joined with 

 its fellow across the middle line by a grey bar or bridge, which 

 springs from the convexity of the crescent, and is pierced from end 

 to end by the central canal. The anterior horn of the crescent, 

 although it varies in shape at different levels of the cord, is, in 

 general, broad and massive, in comparison with the slender and 

 tapering posterior horn. In the lower cervical and upper dorsal 

 region a moulding or projection, forming a lateral horn, springs 

 from the fluted outer side of the grey substance. Within the grey 

 matter nerve-cells are found, sometimes so regularly arranged that 

 they form veritable cellular or vesicular strands. Of these the best 



* The centre or nucleus of reception of a nerve contains the nerve-cells 

 around which its axons terminate; the nucleus of origin of a nerve contains 

 the cells from which its axons arise. 



