24 C. W. M. Poynter 



variation in results. Until a uniform method for measurements 

 is adopted, we are not in a position to express any opinion as to 

 the comparative development of the frontal and parieto-occipital 

 regions. It is even impossible to compare the work of Cunning- 

 ham and Eberstaller, for the former expresses his results as an 

 index, while the latter uses the direct measurements. The most 

 we can say is that the variability of development between the 

 frontal and parieto-occipital regions has been proven by the work 

 of Sergi and others, and that it appears to have an ethnological, 

 if not a sex, value. 



Hitzig (1874), from a comparative study, concluded that the 

 development of the frontal lobe kept pace with the growth of 

 intelligence. While this may be true for comparative studies, 

 it has not proved true for man alone. 



The Fissura Sylvii: The fissura cerebri lateralis (Sylvii) em- 

 braces the fissura Sylvii propria (Retzius) (das ausserer Haupt- 

 stiick der Fissura Sylvii of Eberstaller), the ramus posterior 

 ascendens, ramus posterior descendcns, and two anterior branches, 

 ramus anterior ascendens and ramus anterior horizontalis. 



The variations of the fissure are : Cunningham and others have 

 placed great stress on the direction it takes, i. e., the angle made 

 with the horizontal plane. Retzius does not consider any of its 

 variations especially significant. The termination of the fissure 

 may be by a single limb posteriorly. Retzius found this condition 

 in 30 per cent. Anteriorly either the ramus ascendens or ramus 

 horizontalis may be wanting or the two may be joined to form a 

 " U," " V " or " Y." These variations will be farther discussed 

 with the opercula. Cunningham (1892) and Eberstaller (1890) 

 both found a variation between the right and left sides, the left 

 fissure being longer. The termination of the fissura Sylvii 

 through confluence with some other fissure has not been generally 

 studied. In my table I have collected all the data available, but 

 have not distinguished between the various fissures which may 

 take part in this confluence, viz., sulcus temporalis superior, sul- 

 cus interparietalis and sulcus transversus. 



Sylvian Opercula: These opercula have attracted a great deal 

 of attention because their degree of development has been con- 



368 



