Vice-President’s Address. ry 
is entirely concealed by the neighbouring portions of the 
frontal, parietal, and temporal lobes, which have grown more 
rapidly than the submerged island. The process of covering 
the island of Reil commences with the temporal lobe, which 
grows upwards and outwards, and meets a process from the 
parietal and adjacent portions of the frontal, passing outwards 
and downwards. ‘These processes are known as the temporal 
and fronto-parietal opercula. By the end of the sixth month 
they have met, so as to conceal the posterior half of the 
island. About this time two other smaller opercula begin 
to appear, known as the frontal and orbital. The frontal 
operculum grows downwards and backwards, and the orbital 
directly backwards. The island of Reil is not fully concealed 
until about a month after birth, by which time the four 
opercula completely cover it. The lines corresponding to the 
meetings of the adjacent opercula form the three limbs of 
the Sylvian fissure; the anterior horizontal limb is between 
the orbital and frontal opercula, the anterior ascending limb 
between the frontal and fronto-parietal opercula, while the 
horizontal limb separates the temporal and fronto-parietal 
opercula. It was Broca who first pointed out the existence 
of two anterior limbs to the Sylvian fissure in man; indeed, 
he considered it as constant in the human subject, except in 
the case of imbeciles, idiots, and microcephalic individuals. 
Eberstaller, however, has shown that we may meet with all 
possible gradations from the single anterior limb to the 
Y, V, or U conditions. These variations depend upon the 
degree of development of the orbital operculum. If this be 
absent, only one limb is found; if only feebly developed, the 
single fissure is bifid at its extremity; while, if it be well 
formed, and grow downwards and backwards, so as to touch 
the temporal operculum, two distinct anterior limbs are 
present. 
Broca and Hervé have described in the chimpanzee an 
anterior horizontal and an occasional anterior ascending limb 
to the Sylvian fissure, but Cunningham holds that in this 
they are mistaken, as in both these anthropoids there is a total 
absence of the frontal and orbital opercula, and consequently 
there can be no true anterior limb of the Sylvian fissure. 
VOL. XIL | B 
