THE NERVOUS SYSTEM 



The nervous system is arranged in two divisions, cerebro -spinal 

 and sympathetic. 



The sympathetic nervous system consists of (i) two gangliated 

 cords, right and left, situated on either side of the vertebral 

 column, and (2) three prevertebral plexuses, namely, the cardiac 

 plexus, situated in the thorax ; the epigEistric or solar plexus ; 

 and the hypogastric plexus, the latter two being situated in the 

 abdomen. 



The cerebro-spinal nervous system or axis consists of the ence- 

 phalon and the spinal cord, the former being situated within 

 the cranial cavity, and the latter within the spinal canal. The 

 continuity between these two divisions is established through the 

 foramen magnum. 



The cerebro-spinal axis is central in position, and is connected 

 with the various parts of the body by the cranial and spinal nerves. 

 It is composed of two kinds o\ nervous matter, white and grey. 

 The white matter consists chiefly of nerve-fibres, and the grey 

 matter consists of nerve-cells, with their axis-cylinder processes 

 or axons and dendrites, the pervading supporting tissue in each case 

 being called neuroglia. In the brain the white matter is disposed 

 in the interior as the tnedulla, and the grey matter forms the 

 exterior or cortex. In the spinal cord the white matter is disposed 

 externally in the form of three columns on either side, whilst the 

 grey matter is situated in the interior. 



The cerebro-spinal axis is surrounded by three membranes, or 

 meninges, which, from without inwards, are named the dura mater, 

 arachnoid membrane, and pia mater. 



The Spinal Cord. 



Membranes of tlie Spinal Cord. — ^The membranes are three in 

 number, namely, the dura mater, the arachnoid membrane, and 

 the pia mater. 



Dura Mater. — ^This is the most external covering of the cord. 



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