120 S. WALTER RANSON 



posed of non-medullated fibers and named it the 'Grenzschicht.' 

 Kolliker ('91) has described it under the name of the ''Plexus 

 der Substantia gelatinosa." Ziehen ('99) regarded it as asso- 

 ciated with the caput and not the substantia gelatinosa, and 

 called it the ''dorsalen Grenzplexus des Hinterhornkopfs." It 

 seems probable that most of these vertical fibers are directly 

 asscnciated with the substantia gelatinosa. 



In the thoracic region the stratum zonale contains more ver- 

 tical fibers than in the cervical, and there is no sharp line of 

 separation between it and the tract of Lissauer. It is clear that 

 the fibers of the one pass directly over into the other. The 

 vertical fibers of the 'Grenzschicht' or intermediate layer are 

 especially well-developed in the thoracic region, and while the 

 vast majority of them are non-medullated, there are a few med- 

 uUated vertical fibers to be seen. 



In the lumbar region there is an increase in thickness of the 

 stratum zonale immediately underneath the tract of Lissauer: 

 elsewhere it is represented by a thin layer. Here again it is 

 clearly evident that it serves as a means of connection between 

 the substantia gelatinosa and the tract of Lissauer. The verti- 

 cal fibers of the intermediate layer are slightly more numerous 

 than in the cervical cord, but not so closely packed as in the 

 thoracic cord. 



No mention has been made in this account of the bundles of 

 fibers from the dorsal roots and the posterior funiculus, which 

 pass through the substantia gelatinosa on their way to more 

 ventral portions of the gray substance, since these cannot prop- 

 erly be considered as a part of its fiber complex. 



The substantia gelatinosa in the cat shows the same close re- 

 lation between the stratum zonale and Lissauer's tract. The in- 

 termediate layer of vertical fibers is the same in the cat as in the 

 monkey and shows the same increase in number of fibers in the 

 thoracic region. The same observations may be made on the rab- 

 bit. In the rat the vertical fibers of the intermediate layer tend 

 to accumulate ventrally to the lateral angle of the substantia 

 gelatinosa, especially in the cervical and thoracic segments. 



