Minutes of Proceedings. 199 



man. The anterior part of tlie insula in the ape is on the surface exposed 

 to view and uncovered by opercula. When we compare the insula in 

 man with the submerged portion in the apes, the latter is found to 

 be much smaller in proportion. In the lower apes, the insula is very- 

 narrow, while the longer axis is greater relatively than in the anthro- 

 poids. In the human female, as well as in the anthropoids, the point 

 at which the trunk of the Sylvian fissure appears on the outer surface 

 of the hemisphere is slightly further back than in the male, and this is 

 a retention of the infantile character. The left hemisphere has an 

 average length slightly greater than that of the right. But the Sylvian 

 fissure is considerably longer in the left hemisphere ; and this is 

 true of all periods of growth, and attains its full accentuation in the 

 adult brain. There is apparently no appreciable difference in the 

 length of the fissure in the two sexes, though the contrary has been 

 asserted ; in the ape the fissure is relatively longer than in man. "What 

 is called the Sylvian angle is wider, both in the apes and in man, on 

 the left side than on the right ; and this constitutes at every stage of 

 growth a marked difference between the hemispheres. 



Dr. Cunningham next passes to the fissure of Kolando, which, if it 

 were named after him who first described it, ought rather to be called 

 the fissure of Yicq-d'Azyr. It would best be called the " central" 

 fissure, if that epithet be interpreted as indicating its approximate 

 equidistance from the frontal and occipital poles of the hemisphere. 

 One of the most remarkable points brought out by Dr. Cunningham in 

 relation to the Eolandic fissure in man is the stability of its position on 

 the surface at all stages of growth. It is usually formed in two 

 portions, a lower and an upper, which appear independently, and 

 afterwards unite. ^ In the lower apes a continuous, not an interrupted 

 form of development seems to obtain. 



^ Since tliis Address was written, Dr. Cunningham has sent me the following 

 interesting note in relation to what I have said on the formation of this fissure : — 

 ' ' The development of the fissure in two parts is very significant. The develop- 

 ment of a fissure is hrought about by an intensity of growth of the surface on 

 either side of it ; the surface grows up in the form of two bounding banks. This 

 intensity of surface -growth is, of course, associated with the development of 

 function in the area affected. The district immediately in front of, and behind 

 the fissure of Rolando, is occupied by the motor centres of the lower limhs, upper 

 limbs, and face in that order from above downwards. The appearance of the 

 fissure in two parts probably means the separate appearance of the arm and leg 



R.I. A. MINUTES, SESSION 1895-'96. [20] 



