18 Proceedings of the Royal Physical Socvety. 
Although the island of Reil is entirely concealed in man, 
as already described, yet it is much more highly developed 
than in the apes. Cunningham figures it in the Chacma 
baboon as quite smooth. Waldeyer’ found that in the 
gibbon it is nearly smooth, but generally shows a shallow 
sulcus centralis insule. In the chimpanzee, according to 
Cunningham, there are two oblique fissures dividing the 
insula into three convolutions, while in the orang there are 
three fissures and four convolutions, 
In the human subject they are still more complex, and 
Eberstaller has shown that a remarkable correspondence 
exists between the fissures on the insula and those on the 
outer aspect of the rest of the hemisphere. Thus it is 
divided into an anterior and a posterior part by a fissure 
which has the same direction, and lies in the same plane of 
the fissure of Rolando. Guldberg has suggested for this 
fissure the very appropriate name of sulcus centralis insule. 
The island of Reil in front of this fissure shows three gyri 
which unite below to form the pole of the island. Eberstaller 
calls these three gyri from before backwards gyrus brevis 
primus, gyrus brevis secundus, and gyrus brevis tertius. 
Cunningham suggests for the gyrus brevis tertius the name 
gyrus centralis anterior, as this term would indicate its 
relation to the sulcus centralis insule and also associate it 
with the anterior central or ascending frontal convolution on 
the outer surface of the hemisphere. 
Behind the central fissure of the island of Reil are two 
well-marked convolutions, separated by a fissure which may 
be called the sulcus post-centralis insule. This fissure 
corresponds to the vertical portions of the intra-parietal 
fissure. 
I fear that I must have wearied you with these details, . 
but I trust they have made clear to those not specially 
familiar with this department of anatomy the interesting 
fact, first enunciated by Leuret and Gratiolet, and abundantly 
confirmed by subsequent workers, that the arrangement of 
the cerebral fissures and convolutions in the anthropoid apes 
1 Sylvische Furche und Reil’sche Insel des Genus Hylobates—Sitzungsber. 
der k. Preussischen Akad. des Wiss. Berlin, 1891. 
