TRACT OF LISSAUER 115 



broad. It is more sharply defined medially than laterally, but 

 not very sharply defined on either side. While the transition 

 into the lateral funiculus is somewhat gradual, the tract can not 

 properly be said- to extend into that funiculus. The entering 

 bundles from the dorsal root cut through the dor so-medial angle 

 of the tract; and the small part which is thus cut off is spread 

 out somewhat diffusely in the posterolateral angle of the cuneate 

 fasciculus. Bundles of non-medullated fibers can be traced into 

 the tract of Lissauer from the dorsal roots. None of my prepa- 

 rations show medullated fibers from the dorsal roots entering 

 the tract. But this may be due to the intimate relation of the 

 entering root to the tract. As the bundles of root fibers pass 

 through the tract some of them might separate from the others 

 and become constituent fibers of the tract without being easily 

 detected. 



In the eighth thoracic segment the columna posterior is long; 

 and the substantia gelatinosa is about the same distance from 

 the surface as in the seventh cervical segment. But the space 

 between the substantia gelatinosa and the surface of the cord 

 is not fully occupied by the tract of Lissauer which lies close to 

 the surface and is some distance from the substantia gelatinosa. 

 The tract is very diffuse without sharp limits in any direction. 



In the fifth lumbar segment the tract is located on the lateral 

 extremity of the substantia gelatinosa and is short and broad. 

 It is better defined medially than laterally ; but the lateral exten- 

 sion which is well developed is outward along the surface of the 

 cord rather than along the lateral border of the columna posterior. 

 The entering rootlets pass through the dorso-medial angle of 

 the tract, cutting off a small part, which lies as a thin band along 

 the surface of the cord in the dorso-lateral angle of the cuneate 

 fasciculus. Non-medullated fibers can be traced from the roots 

 into the tract of Lissauer, but not in such a diagrammatic man- 

 ner as in the cat and the monkey. I have not been able to trace 

 medullated fibers from the dorsal root into the tract. 



The structure of the tract is the same in the rabbit as in the 

 monkey and the cat. 



The tract of Lissauer in the squirrel is very similar to that in 

 the rabbit and requires no special description. 



