1902.] Descending Spinal Tracts in the Mammalian Cord. 117 



the cord is ripening for the second operation. We have, however y 

 obtained thirteen successful complete experiments : in these the shortest 

 interval has been 260 days, the longest 568 days. Among these is 

 included two in which, for special reasons, the partial cross-lesion of 

 the cord was made precedent to the total transection. ' 



Results. 



The spinal segments examined as sources of aborally-running fibre- 

 systems have been posterior cervical, anterior thoracic, mid thoracic, 

 posterior thoracic, and anterior lumbar. From all these regions our 

 experiments demonstrate that copious aborally-running fibre-systems 

 spring. Thus, the accompanying fig. 1 shows, for instance, tracts of 

 fibres in the 5th lumbar segment which have their origin in cells of the 

 2nd thoracic segment. 



Fig. 1. 



Cross-section of the cord of the dog at a level in the anterior part of the 5th 

 lumbar segment ; Marchi preparation. The section reveals the topography at 

 that level of the aborally -running fibre-system of the 1st and 2nd thoracic 

 segments. The 8th cervical segment of the cord had been completely exsected 

 and ablated. A partial translesion (rather more than a semi-section) was made 

 the left half of the 3rd thoracic 568 days subsequent to the removal of the 8th 

 segment. The exact extent of this second lesion was determined subsequently 

 by microscopic examination in serial preparations, and its limits will be 

 described and figured in a fuller communication. The dots indicate, in a way 

 mentioned in the text (p. 120), the density and extent of the degenerate tracts 

 of fibres. L = left side ; K. = right side. 



Speaking generally, of the fibres composing the aborally-running 

 systems springing from the grey matter of the spinal segments 



