Clark, Comparative Anatomy of the Insula. yi 



sad but with the exception of the transinsular none of them 

 reach the ventral margin. The area common to all the gyres 

 of the preinsula, and from which they all appear to spring, is 

 usually the part most elevated and is called the pole of the insula. 

 Eberstaller (17^ 741) says that the " limen insulse " (pole) is 

 found only or in a certain form in the human brain. 



But for the unusually elevated pole in this specimen, Fig. 

 5 might be said to represent a nearly typical insula. The pre- 

 insula usually possesses three gyres of which the first (the one 

 most cephalic) and the third are usually the best developed and 

 these are trequently subdivided dorsad by short fissures. The 

 postinsula seldom possesses more than two gyres the first of 

 which is usually the larger. These gyres are united ventrad 

 and are always longer than those of the preinsula. Eberstaller 

 (17, 741) says the first gyre of the preinsula is the largest and 

 strongest and that the second gyre is usually weakly developed. 

 The postinsulas shown in Figs. 3 and 4 exhibit a peculiarity 

 which is very striking when compared with the usually simple 

 character of the area. The three small elevations of Fig. 3 

 and the one in Fig. 4 dorsad belong to the postinsula. It is pos- 

 sible that the shallow furrows separating these eminences may 

 have been caused by arterial pressure. Fg. 3 also shows 

 the relation of the insula to the medicornu. The specimen shown 

 in Fig. 5 is remarkable for the unusual elevation of the pole. 

 As previously stated this condition is probably the result of some 

 peculiarity in the development of the brain stem. 



In 1887 Waldschmidt (gi, 375) said the insula was larger in 

 educated persons. There are many facts favorable to this view 

 but it lacks confirmation. 



Eberstaller and Cunningham have each called attention to 

 the apparently intimate relation of the transinsular and central 

 fissures. These fissures are very constant in the human brain, 

 they lie in the same plane, they take the same general direction 

 and they appear in the fetus at about the same time (5-6 mo.). 

 Eberstaller (17, 749, 1887) says: "The cephalic insula is con- 

 nected wholly with the frontal lobe, the caudal insula with that 

 portion just caudad of the central fissure." 



