The Nervous System. "2Go 



as the sympathetic ; one part of the latter, the gangliated 

 cord, runs under the arch of the ribs and back as far as the 

 loins ; to this cord the white ramus runs, and establishes a 

 communication between the cerebro-spinal and sympathetic 

 system ; moreover, in this branch are the nerves which con- 

 strict all the bloodvessels in the body. A careful study 

 of Fig. 24 is necessary for clear elucidation of the arrange- 

 ment of the spinal nerves. 



Arrangement of the Cord.— If a cord be suitably prepared, 

 it is found to consist of a superior, lateral, and inferior 

 column, each divided by a longitudinal groove. On the 

 superior and inferior surface is a fissure : the inferior fissure 

 is wide, and does not reach down to the centre of the cord ; 

 the superior fissure is very narrow, and so deep that it runs 

 down into the central portion of the cord. 



On making a section of the cord, it is found to be made 

 up of both white and grey matter, the latter internally 

 placed, forming the medulla, is arranged something like 

 two commas placed back to back, the tail of the comma 

 being uppermost; the tail of the comma corresponds to 

 the incoming sensory fibres, the head of the comma to 

 the outgoing motor ones. The two commas are connected 

 by a band of grey matter, known as the commissure, in the 

 centre of which is a canal. 



Speaking roughly, we may say that the white substance 

 of the cord is made up of fibres, the grey substance of 

 nerve cells. The white substance is not the same thick- 

 ness throughout, the upper portion of the cord containing 

 more white matter than the lower portion. In the same 

 way, the grey substance is not the same thickness nor the 

 same shape throughout the length of the cord. This grey 

 substance is very important. We shall have to show that 

 directly or indirectly both the superior and inferior nerve 

 roots communicate with it. The nerve cells composing it 

 are multipolar and of considerable size, each containing 

 nuclei with nucleoli. It has been ascertained that the 

 nerve cells of the grey matter are unequally distributed, 

 and can be grouped according to their position ; thus, in 



