240 



DR. O. E. NICHOLLS ON TDE 



The examination immediately revealed the fact that for a 

 considerable distance upon the narrow crest of the bone there 



Text-figure 1. 



rv.c. 



c Jfr d 



In a the position and extent of the neural canal, as seen typically in lateral view, of 

 the urostyle of Sana tigrina are represented, XlJ; h, c, d represent variations 

 not infrequently found, also Xl^- In a',d' the urostyles a and d are repre- 

 sented as seen from ahove, but the size of the dorsal opening of the neural 

 canal and the width of the dorsal furrow (iu which lies the free end of the filum 

 terminale) are greatly exaggerated. 



n.c. indicates a bristle inserted in the neural canal and emerging dorsally. (In b 

 the neural canal within the urostyle is short and wide, and the extreme posi- 

 tions, forward and backward, of the bristle a,re shown.) Actually, within the 

 canal, the bristle is indicated by an interrupted line. 



The black line f.f.t. indicates the extent of the dorsal furrow (the uncovered pos- 

 terior extension of the neural canal) which lodges the end of the filum terminale; 

 in d (and d') a part of this furrow has been roofed in, leaving above it only a 

 very shallow groove, d.f., connecting an anterior opening of the neural canal, 

 n.c.', with the more posterior opening, n.c. 



