116 S. WALTER R ANSON 



THE TRACT OF LISSAUER IN THE ALBINO RAT 



In the albino rat the substantia gelatinosa Rolandi is very 

 massive, and differs in shape and position from that in the ani- 

 mals already studied. It does not vary much in shape from 

 segment to segment, as in the other animals, but in the cervical, 

 thoracic, and lumbar cord alike it. reaches almost to the surface 

 and is only slightly curved. In other words, it is spread out 

 along the dorsal surface of the cord (fig. 11), from which it is 

 separated by a very thin band of fibers representing the tract 

 of Lissauer. The slight curvature brings the two extremities of 

 the substantia gelatinosa somewhat farther from the surface. 

 The superficial band of fibers has the same structure as the tract 

 of Lissauer in other animals, consisting of scattered fine medul- 

 lated fibers and closely-packed non-medullated ones. This band 

 is very small in proportion to the size of the cord, and especially 

 in proportion to the size of the substantia gelatinosa. At the 

 lateral angle of the substantia gelatinosa the tract becomes 

 continuous with an area which lies just lateral to the substantia 

 gelatinosa and the caput of the columna posterior. This area in 

 the lateral funiculus contains scattered small and medium-sized 

 medullated fibers and is crowded with fine non-medullated axons. 

 It has, in other words, the same structure as the lateral extension 

 of the tract of Lissauer in the monkey. In the rat, due to the 

 excessive development of the substantia gelatinosa, the tract 

 of Lissauer proper has been reduced to a narrow strip between 

 the substantia gelatinosa and the surface of the cord. The 

 main bulk of the tract is located in the lateral funiculus in the 

 region occupied in some other animals by a more or less diffuse 

 lateral expansion of the tract. The tract of Lissauer and its 

 lateral expansion are much the same in each of the three princi- 

 pal regions of the cord. 



