266 S. WALTER RANSON 



teristic content is an enormous number of fine vertically coursing 

 non-medullated fibers. 



Before taking up the account of the course taken by the dorsal 

 root fibers as they enter the cord it will be desirable to call atten- 

 tion to the \'ariations in shape and topography of the tract of 

 Lissauer at different levels in the cat's cord. In the cervical 

 region as illustrated by the seventh cervical segment (fig. 1) the 

 tract is long and narrow, since the substantia gelatinosa is at 

 some distance from the surface of the cord and the tract fills the 

 entire apex of the posterior cornu. Throughout the entire tho- 

 racic regidn of the cord (fig. 3, T. 8) the posterior cornu is not 

 well developed; the substantia gelatinosa is placed a long dis- 

 tance from the surface of the cord; and the cone-shaped Lissauer's 

 tract which caps it is also some distance removed from the sur- 

 face. The apex. of the cone is connected with the surface by a 

 septum containing few fibers; occasionally isolated portions of 

 Lissauer's tract are seen along the medial side of this septum. 

 In the lumbar cord (fig. 4, L. 5) the substantia gelatinosa has 

 approached the surface; and the tract of Lissauer, which fills the 

 interval between it and the surface has become short and wide. 

 In the sacral region (fig. 5, S. 1) the substantia gelatinosa has 

 flattened out laterally and the tract of Lissauer occupies a short 

 but wide interval between it and the periphery of the cord. 



The size of the tract varies somewhat from level to level and 

 seems to be roughly in proportion to the size of the nerve roots 

 entering at that and adjacent levels. The first sacral segment 

 seems to be an exception to this rule. Although its entering 

 rootlets are larger, it presents a Lissauer's tract somewhat smaller 

 than that in the fifth lumbar segment. These facts would be 

 easily explained if we assume that the majority of the non-medul- 

 lated fibers in the tract are short ascending fibers from the dorsal 

 roots. The small rootlets of the lower sacral segments would 

 then contribute fewer ascending fibers to the tract in the first 

 sacral segment, than would be contributed by the large rootlets 

 of the upper sacral and last two lumbar nerves to the tract in 

 the fifth lumbar segment. The ascending fibers must be rela- 

 tively short, however. Otherwise there would be a steady increase 



