70 W. ELAXLAND BENHAM. 



It appears to me particularly interesting to find in the chim- 

 panzee a condition so closely resembling that on man's right 

 side. 



Cunningham regards the inferior frontal convolution of 

 the ape as representing non-covered insula, and the " sulcus 

 fronto-orbitalis " as the horaologue of the anterior limiting 

 sulcus of the insula, and compares it with foetal human brains 

 at a certain stage. But the position and relations of the 

 fronto-orbital fissure (e. o.) with regard to the " anterior 

 limb " of Sylvius (limit of fronto-parietal operculum) seem to 

 me to be very different. In most of the chimpanzees it passes 

 upwards from the orbital surface of the frontal lobe some 

 distance in front of the anterior end of the Sylvian fissure, 

 and curves upwards and forwards, extending considerably above 

 the so-called " anterior limbs." It is easy to understand how 

 the folding backwards — formation of orbital operculum — in 

 the fig. 9, pi. iv of Cunningham's memoirs would give rise to 

 the state of things represented in his fig. 1 of the same plate 

 representing human foetal brain. 



Here the fissure supposed to correspond with the fronto- 

 orbitalis joins the '' anterior ascending limb " of the Sylvian 

 fissure, and then curves backwards. From the facts referred 

 to above, and represented in the photograph (fig. 8), it seems to 

 me that the sulcus fronto-orbitalis may have some other 

 meaning. May it not be part of the system of orbital furrows 

 which has extended upwards ? 



9. Frontal Lobe. 



A system of furrows, more or less parallel to, and in front 

 of, the fissure of Rolando, constitutes the '' praecentralis,^' 



This prsecentral fissure arises, according to Cunningham, in 

 three pieces — vertically, a " prsecentralis inferior,'^ and a " praj- 

 centralis superior," with a horizontal ramus, which is usually 

 connected with the upper part of the former. 



On the right hemisphere of ^'Sally's" brain (figs. 11, 12) the 

 sulcus prsecentralis inferior {p. c. i.) is divided into an upper 

 and a lower portion by a submerged gyrus situated just above 



