CANAL IN THE SPINAL MARROW. 30l 



veTed in the year 1803, in the medulla spinalis of the horse, 

 bullock, sheep, hog, and dog ; and should it appear to you 

 deserving of being laid before the Royal Society, I shall feel 

 myself particularly obliged, by having such an honour coni- 

 fer red upon me. 



Upon tracing the sixth ventricle of the brain, which cor- communicat- 



responds to the fourth in the human subject, to its appa- «»g with one* 



r . , ', theventneles 



rent termination, the calamus scnptonus, I perceived the ofthe brain> 



appearance of a cana}, continuing by a direct course into 

 the centre of the spinal marrow. To ascertain with ac- 

 curacy whether such structure existed throughout its whole 

 length, I made sections of the spinal marrow at different 

 distances from the brain, and found that each divided por- 

 tion exhibited an orifice with a diameter sufficient to admit 

 a large sized pin ; from which a small quantity of trans- 

 parent colourless fluid issued, like that contained in the and containing 

 ventricles of the brain. The canal is lined by a membrane a fluid - 

 resembling the tunica arachnoidea, and is situate above 

 the fissure of the medulla, being separated by a medullary 

 layer : it is most easily distinguished where the large nerves 

 are given off in the bend of the neck and sacrum, imper- 

 ceptibly terminating in the cauda equina. 



Having satisfactorily ascertained its existence through the A continuate 



whole length of the spinal marrow, my next object was to tube the whole 



■i . . lip • length of the 



discover whether it was a continued tube from one extremity spinal mareow, 



to the other : this was most decidedly proved, by dividing 



the spinal marrow through the middle, and pouring mer- . 



curyinto the orifice where the canal was cut across, it passed 



in a small stream with equal facility towards the brain (into 



which it entered), or in a contrary direction to where the 



spinal marrow terminates. 



By many similar experiments, I have since proved, that a The fluid has 



free communication of the limpid fluid, which the canal a free comn \ u * 



. . , t A , . iii „ nication with 



contains, is kept up between the bram and whole extent of the brain. 



spinal marrow. I have consulted the most celebrated au- 

 thors on comparative anatomy, but do not find any such 

 structure of those parts described ; and as it is not known to 

 you, I may presume, that it has not been before taken 

 notice of. I have the honour to be, 



Sir, your obedient faithful servant, 

 Veterinary College, Nov. 26, 1808. WM, SEWELL. 



