THE NERVES OF MOTION AND OF SENSATION, AND THE BRAIN. 257 



sistence or structure into which nerves can be traced : and through the whole column 

 of the spinal marrow, up to the fifth and portio mollis of the seventh nerves of the 

 head, the cineritious matter is superimposed on the columns and nerves *. 



Between the lateral columns, the cineritious matter lies deep. Upon raising it, the 

 anterior or motor columns are seen (fig. 4. d, d.). In essential circumstances they 

 resemble the lateral columns, and they are distinct from them. The cineritious 

 matter occupies a portion of the space between them ; and as to the remaining part, 

 the line of separation is distinct, and the surfaces are unbroken. 



By the manner in which the dissection has been made, the posterior portion of the 

 spinal marrow being raised, as it were, out of the heart of the cord, the remaining 

 parts fall flat, and the lateral and anterior columns separate. 



Having distinguished the columns which form the spinal marrow, their natural 

 sulci, their proper connexions, and the distribution of the cineritious substance be- 

 tween them, we have in the next place to observe how these columns are arranged, 

 and what change they undergo in the upper portion of the cord, called medulla ob- 

 longata. We approach from below the same parts which we looked upon in their 

 relations with the brain in the last paper. 



We must now have before us a portion of the spinal marrow with the medulla ob- 

 longata attached to it, and proceed with the dissection. 



The parts being presented in the same aspect as before, we raise the two posterior 

 columns, separating them from the others at the intervening cineritious matter. At 

 the back of the medulla oblongata we find the posterior columns diverging, and 

 forming the triangular space of the fourth ventricle; this space is laid open on 

 tearing up the pia mater, which connects the cerebellum with the medulla oblongata. 

 Each of these columns is now seen to consist of two, the outermost the larger, and 

 that towards the central line the smaller, and in shape pyramidal -(-. Following up 

 these diverging columns, we recognise them to be the processus cerebelli ad medul- 

 1am oblongatam. These great tracts, which form a large portion of the spinal mar- 

 row, are now seen to bear relation to the cerebellum. 



The posterior tracts or columns being raised, we have only the lateral and anterior 

 columns, which belong to the cerebrum, to attend to. And here is the interesting 

 part of this communication. 



Once more observing the layer of cineritious matter, we brush it off from the 



* It is easy to trace the roots of the sensitive portion of the spinal nerve into the lateral column. It should 

 be observed at the same time, that in raising the posterior columns, by insinuating an instrument into the cine- 

 ritious intermediate substance, there is a more intimate attachment of the medullary substance of the posterior 

 column at its outer edge and in the line of the origins of the nerves. It is not impossible, therefore, that the 

 posterior column may be connected with the sensitive root of the spinal nerves, though hitherto I have not 

 traced the fibres. 



t This subdivision of what I have called the posterior column of the spinal marrow is to be traced in the 

 whole length of the spinal marrow. 



2l2 



