92 Journal of Comparative Neurology and Psychology. 



Number of Segment. Diameters in millimeters 



mid-way 4 3 



The dorso-ventral diameter of the 32nd segment includes 

 the depth of the sinus rhomboidahs and the fissura ventrahs. 

 Between the two there is Httle more than the gray commissure 

 of the lumbar cord. 



Examination of the stained sections reveals that both the 

 gray and the white substance of the cord take part in produc- 

 ing the segmental enlargements. Figures 3 and 4, which are 

 camera drawings, show that that gray figure is larger at the 

 levels nearer the fusion of the nerve roots than it is mid-way 

 between the nerves of adjacent segments. 



From both transverse and longitudinal sections (Fig. 2), it is 

 apparent that the white substance plays a somewhat greater role 

 in forming the swellings than the gray. For quite an extent mid- 

 way between the adjacent nerve pairs of the longer segments 

 there are no fila radicularia coursing upon the pia or evident 

 beneath it. If ventral and dorsal root axones are connected 

 with this region of the segment, as no doubt they are, they 

 must course within the white substance, making their exit and 

 entrance at levels nearer the levels of the respective nerve roots 

 to which they belong. Just as the fila emerging or entering 



