48 THOMAS DWIGHT ON 



that in front of the fissure of Rohuido we find in order, first, the anterior suhcentralis 

 then the praecentralls, then the anterior limb of the Sylvian, and finally the fronto- 

 orhitalis (of Kiikenthal and Ziehen'). The snine series on the right is found by the 

 interpretation offered above. 



Fissure of Rolando. Exceedingly plain and diagrammatic on the left, sliowing 

 very clearly the two knees. The upper end opens on the mesial surface. The lower 

 does not reach the Sylvian fissure. The same is essentially true of the right fissure, 

 but the knees are less well marked. The fissure cuts the median line at a distance 

 of about 6.5 cm. measured directly backward from a. sti-aight line at the front of the 

 bi'ain. The frontal lobe must be described separately on the two sides. The left is 

 taken first, as more resembling the human brain. The anterior centi'al ct)nvolution 

 is much larger than the posterior. It is directly continuous with the three frontal 

 convolutions, the first at the side of the median fissure, the second a little above 

 the middle, and the third at the lower end. The middle convolution divides the 

 praecentral fissure into a larger inferior and a smaller superior part. Each of these 

 receives a sulcus frontalis ; the superior is short, ending in a bifurcation ; the inferior 

 is long and complicated, running to the very front of the brain where it ends with a 

 sweep inward. There is another fissure (?pl. 10, fig- 1) very like one described by 

 Benham in " Sally " wliich also has its upper end internal to the frontalis siqjerior. 

 It is well marked and deep, with an external branch. It is not clear whether it is 

 to be called a continuation of the sulcus frontalis primus or a frontalis mesialis. 

 The second frontal convolution fuses with the fii^st at the front of the brain. The third 

 frontal convolution arises from the very lower end of the anterior central, runs at 

 first upward, then, turning forward, it surrounds the bifurcated anterior limb of the 

 Sylvian fissure, forming a rudimentary but distinct 2^'^'''>'^ triangularis. In front of 

 this, it rises again to loop round the sulcus orhito-frontalis, which is a striking fis- 

 sure. The inferior or orbital surface of the frontal lobe is not easily understood. 

 A small fissure running to the mesial surface must represent the olfactory fissure. 

 The general direction of the other fissures is forward and inward. The sulcus orhito- 

 frontalis bounds it externally but behind runs into its inferior surface. 



The right frontal region is very different in some important respects. The 

 anterior central convolution is larger than the left one, consequently its predomi- 

 nance over the posterior is more marked. The second frontal convolution is very 

 large in its first pai-t. The superior praecentral sulcus is longer than on the left. 

 The superior frontal sulcus runs forward almost to the orbital border of the brain. 

 This is a very uncommon development of this farrow wiiich I do not remember to 



' Untersuchungen liber die grosshirnfurclien der primaten, Jena, zeitselir., vol. 20, 1894. 



