SPINAL MARROW. 331 



anatomists, and even positively denied by some. There are 

 other places where the fasciculi of the spinal marrow seem to 

 cross from one side to the other, but the fact is not yet verified 

 sufficiently. 



The existence of canals in the spinal marrow has beefi from 

 time to time announced ;* though authors differ much in the ac- 

 counts of their position and extent. When such an appearance 

 is presented, it is supposed, by some, to be either the result of 

 disease or of accident, with the exception of a small one of eight 

 or nine lines long, which communicates at one end with the 

 fourth ventricle, and is shut up at the other.t 



Valentine asserts that the primitive fibres of the nerves, which 

 join the spinal marrow, do not terminate there, but pass on to 

 the brain.J In the spinal marrow of a child, it is very easy to 

 divide it by tearing into threads, running its whole length; these 

 threads do not seem to have any determinate number, but to be 

 regulated by the healthy consistence of the spinal marrow, and 

 the patience with which the process is pursued. If a spinal 

 marrow has been macerated for some years in spirits, it may 

 be broken or split up into radii, from the centre to the cir- 

 cumference, like a tree, and these sections divided into thin, 

 short, flat laminee adhering to, or anastomosing with such as are 

 contiguous to them. Muller found a similar arrangement in the 

 spinal marrow of the Petromyzon Marinus, though he has 

 never seen it in any other animal. 



The Spinal Marrow sends out from its sides thirty pairs of 

 nerves, which, like the vertebra, are arranged into cervical, 

 dorsal or thoracic, lumbar and sacral. Of these there are eight 

 cervical, one of which, from its escaping between the occiput 

 and the first vertebra, is most usually designated as sub-occipital, 

 and, therefore, the number of the cervical nerves is reduced to 

 the same with that of the vertebrae, to wit, seven. There are 

 twelve pairs of dorsal nerves, five of lumbar, and five of sacral. 

 Occasionally, there is a sixth sacral nerve on each side, which 

 augments the number of spinal nerves to thirty-one pairs. 



Every spinal nerve is formed from two roots on the same 



* Gall, Portal, Morgagni, 



t Mcckel, p. 605, vol. ii. Bichat, vol. Hi. p, 128, 



t Muller's Report on Nervous System, 



