70 Journal of Comparative Neurology. 



wholly superficial, is gradually covered more or less completely 

 by converging folds of the adjacent regions. The insula thus 

 becomes a subgyre, while the operculum, preoperculum, sub- 

 operculum and postoperculum are supergyres." 



The adult human insula is always sharply demarcated by 

 the surrounding circuminsular fissure {rigolcs, Broca). Its posi- 

 tion is generally in a plane nearly parallel with the lateral sur- 

 face as shown in Figs. 3 and 4. An exception is shown in Fig 5. 

 In this specimen the gyres form a plane nearly perpendicular 

 to the lateral surface. This is a condition found in the sheep, 

 the pig (12, 9), the calf, and some horses, and is believed to be 

 due to some peculiarity in the development of the brain stem. 



In the adult, the insula is a large broad eminence, the sur- 

 face of which is richly convoluted. It generally possesses from 

 four to six gyres diverging cephalad, dorsad and caudad and 

 producing an appearance not unlike that of a fan. The num- 

 ber of gyres is subject to considerable variation even in the two 

 insulas of the same brain. The brain of Guiteau, the assassin 

 of Garfield, showed marked peculiarities in this respect. Ac- 

 cording to Spitzka (55, 3^6) the left insula contained seven fis- 

 sures and eight gyres, while the right had only five fissures and 

 six gyres. It will be noticed that the right insula had its full 

 complement of fissures and gyres while the left exceeded it by 

 two. Another case markedly different from this one has also 

 been reported by the same author. It. like the preceding, is 

 that of a murderer. He says, the left insula had " fewer and 

 flatter gyri than that [six gyri] of the right side, and was 

 not far different from that of an orang in my possession." In 

 all normal brains, the left insula is said to be larger. 



The insula is usually quite deeply fissured and is always 

 divided into two plainly unequal parts. This division is pro- 

 duced by a deep fissure extending dorso-caudad from the ven- 

 tral side — where it is deepest — to the dorsal margin where it 

 connects again with the circuminsular. This forms a cephalic 

 part, prcinsula, and a smaller caudal one, postinsida. The pre- 

 insula is not only larger but contains more gyres. All of the 

 fissures of the insula communicate with the circuminsular dor- 



