258 SIR CHARLES BELL ON THE RELATIONS BETWEEN 



lateral columns. This grey matter may be traced into the fourth ventricle, ex- 

 tending over the parts to be presently described, and over part of the roots of the 

 fifth pair of nerves. It constitutes one sheet of matter from the cauda equina to 

 the roots of the auditory nerves, and forms a grand septum between the anterior 

 and lateral part of the spinal marrow which belongs to the cerebrum, and the pos- 

 terior columns which are related to the cerebellum. 



Union of the lateral Columns in the Medulla Oblongata. 



On brushing away the cineritious matter from the cerebral portion of the spinal 

 marrow, we recognise the two lateral columns. Upwards, or towards the brain, 

 each of these columns has a double termination ; first, in the root of the fifth nerve ; 

 and secondly, in the union of the columns, or, in other words, in their decussation. 



These columns lie separate in the spinal marrow ; but having ascended to the 

 medulla oblongata, they fall together, and form one round column something less 

 than half an inch in length. On tracing this united column upwards they are dis- 

 entangled, but do not separate, for they now constitute those processes of the cere- 

 brum which, in a former paper, we traced down from the back of the crura cerebri 

 (fig. 5. E, E; fig. 6. A, A.). 



On observing the portion of the united columns, the appearance is very much that 

 which is presented by the union of the optic nerves ; that is, however, rather when 

 the part is thoroughly hardened in spirit : when it is somewhat more pliant, we can 

 trace the filaments of one side into the column on the other side*. The decussation 

 is the most perfect of any to be demonstrated in the brain and nerves. 



Reverting to the statement in the former paper, that a septum divides the right 

 and left sensitive tracts where they are seen in the fourth ventricle, and that in 

 tracing that septum downwards it terminates at the point of decussation of these 

 tracts : I have now to add, that the septum does not absolutely terminate, that it 

 splits to permit the oblique course and decussation of the filaments of these columns. 

 Thus separated at the union of the columns, the septa unite again below, and may 

 be followed downwards into that connexion which binds the posterior portion of the 

 spinal marrow to the anterior columns. 



It remains a desideratum to know what is the nature of those fibrous septa which 

 intervene and divide the longitudinal tracts of nervous matter. But whatever may 

 be determined on this point, it is obvious that they form a perfect link or bond of 

 union and mechanical strength, extending from the pons to the cauda equina. Around 

 the commissures the fibres of these bands are especially interwoven -}-. 



* Much of the anatomy, as I have here described it, may be made out in the recent parts. But it will be 

 easier and more satisfactory, when the parts are soft, to drop them into spirits, so that the surfaces as they are 

 exposed may be hsirdened and prepared for further dissection on a succeeding day. 



t The true distinctions between the columns in the spinal marrow may be made, as we did those of the 

 medulla oblongata, by observing the splitting of the septa. From the circumstance of the columns scaHng off 



