DR, C. E. BEEVOR AND PROFESSOR Y. HORSLEY OX A 
154 
Proceeding from the best known of these to those which hitherto have escaped 
especial notice, we will commence with the fissure of Rolando. 
The fissure of Rolando, in all the species of Monkey on which we have experi¬ 
mented, runs outwards, forwards, and downwards, forming an angle of 50° to 55' with 
the mesial margin of the hemisphere. In its course it presents the following changes 
of shape, which in our experience are perfectly constant. Thus, for the uppermost 
quarter of its extent it presents a distinct, though slight, curve with the convexity 
forwards; in the next, i.e. the second quarter, it is slightly curved, with the convexity 
in the opposite direction, viz., posteriorly ; and this curvature, concave anteriorly, 
i‘uns down into the third quarter, in which part of its course the fissure presents a 
well-marked bend forwards. To this bend we would now direct especial attention, for 
it can be demonstrated to exist perfectly distinctly in Man and most Monkeys. 
Further, in the Monkeys we have examined, this bend is situated, as we have already 
said, in the third quarter of the fissure ; its apex or central point is rounded, and is just 
above the horizontal level of the lower end of the intra-parietal sulcus, while, at the 
same time, it is well below the level of the highest point of the praecentral sulcus. 
From the apex of this bend the fissure of Rolando in its lowest fourth slopes almost 
vertically downwards (vertically signifying at right angles to the longitudinal fissure) 
towards the Sylvian fissure. 
The prcecentral sulcus is directed upwards and distinctly backwards from the base 
of the ascending frontal convolution, which it limits anteriorly. Just before it reaches 
the level of the central point of the fissure of Rolando, it bifurcates into two horizontal 
limbs; the anterior and longer runs forwards, being slightly curved with the concavity 
downwards; the posterior, on the other hand, is directed upwards as well as back¬ 
wards, and is extremely short, very rarely exceeding 2 mm. in length. The main 
stem of the sulcus presents a double curve, the upper half having a slight convexity 
backwards, while the lower half is markedly curved forwards. In this way the 
ascending frontal convolution is most narrow opposite the posterior superior limb of 
this sidcus, while below it widens broadly. 
Superior Frontal Sulcus. —In December, 1883, Professor Schafer published in the 
‘ Journal of Physiology ’ an account of the brain of a Macacque Monkey, which was 
shown by Professor Ferrier at the International Medical Congress in London, in 
which account he drew attention to the existence of a small, but definitely marked, 
sulcus on the upper portion of the frontal lobe, having an antero-posterior direction, 
and dividing into two parts the surface of the brain between the upper end of the 
prsecentral sulcus and the mesial margin of the hemisphere. This small sulcus lies 
just behind the line of direction upwards of the vertical stem of the prsecentral sulcus. 
Professor Schafer provisionally named this sulcus x. 
We venture to think that this small sulcus is nothing less than the representative 
of the posterior extremity of the superior frontal sulcus of Man, and that, therefore, 
the portion of brain above it must be looked upon as the first or superior frontal con- 
