120 Descending Spinal Tracts in the Mammalian Cord. [Nov. 5, 



These are less numerous. We defer detailed description of them, 

 together with further detailed description of the ventral and lateral 

 tracts above-mentioned, until a fuller communication dealing with the 

 whole subject. The general features of the topography can be gathered 

 better from the two accompanying figures than from any even lengthy 



Fig. 3. 



R. 



Cross-section of the spinal cord of the dog at the leyel of the anterior part of the 

 4th lumbar segment : Marchi preparation. The section reveals in leCt half of 

 the cord the topography at that level of the aborally-running fibre-systems 

 arising in perikarya of the grey matter of the left half of the 6th and 7th 

 cervical segments. Total transection of the cord had been performed through 

 the 8th cervical segment 268 days subsequent to left semi-section at the 5th 

 cervical segment. Thirteen days only was allowed for the development of the 

 degeneration after the second lesion. The degeneration may not therefore 

 appear so extensive as it might have done later, but its localisation is probably 

 the more precise. The exact extent of the semi-section was found by subse- 

 quent microscopic examination in serial preparations to amount almost accu- 

 rately to a full section of the left half of the cord ; the detailed limits will be 

 described in a fuller communication. The degeneration in the right half of 

 the lumbar cord figured includes aborally-running fibres derived not merely 

 from the spinal cervical grey matter, but from bulbar and cerebral cources as 

 well ; and these are practically inextricably commingled one with another. 

 The dots signify, in the way mentioned in the text below, the density and 

 extent of tbe degenerations. L = left side ; E- = right side. 



textual description. All the figures have been drawn with the camera 

 lucida upon squared proportional paper, and the squares on the paper 

 have been made to correspond with squares in an engraved eye-piece. 

 All the drawings are to exactly the same scale. The dots signify 

 degenerate nerve-fibres, but the number of dots does not of course 

 represent the absolute number of degenerate fibres, but falls far short 



