68 



Journal of Comparative Neurology. 



above statement. The caudal one of the four fissures on the 

 normal insula is never, so far as the writer has been able to 

 learn, "larger and deeper " than the transinsular fissure which 

 is cephalad of it and the observations of Cunningham (14, 347- 

 348) in 1 89 1 seem to show pretty conclusively that even when 

 three fissures are present on this area, the caudal one is usu- 

 ally in the postinsula. 



In the spring of 1890 the writer became convinced, as the 

 result of the study of the comparative anatomy of this region, 

 that future investigation would show that, barring the circum- 

 insular fissure, the transinsular, which is doubtless the most 

 constant and best, defined of the fissures on this area, would be 

 found to be the first to appear after the circuminsular and that 

 its homologue exists in some other animals at least. The 

 following table compiled from Cunningham, 1891 (14, 347-348) 

 seems to prove that this really is the order of development in 

 the human fetus. The brains enumerated below range from 

 five to six and a half months. 



State of Development of Insula. 



Insula perfectly smooth 



" with transinsular fissure 



" " " f. and the one cephalad 



" " " f. one cephalad and one f. caudad 



Totals 



Transin- 

 sular f. 

 present. 



18 



This same author (14^ 347) says: " Furthermore, there is 

 good reason to believe that in the development of the sulci and 

 gyri the right insula is usually in advance of the left, and also 

 that the process is greatly retarded in the female brain." The 

 first part of the above statement of Cunningham, while appar- 

 ently borne out by the table, seems remarkable inasmuch as 

 the left insula in the normal adult as usually larger than the 

 right. 



In 1892 Cunningham (15, 15 summary) said: "In the adult 

 brain the insula is proportionately longer in the male than the 

 female. At all periods of growth it would seem that the insula 

 is relatively longer on the left side than on the right side. In 



