110 LECTUEE IV. 



Turning from tlie anterior central convolutions in a forward 

 direction, we usually find the whole frontal lobe covered with a 

 number of convolutions, which generally stand more or less per- 

 pendicular to the anterior central convolution, that is, more or 

 less horizontal. The convolutions nearest to the longitudinal 

 fissure mostly proceed from the beginning of the central con- 

 volution, so that, to a certain extent, they appear as an 

 appended lobe. We might fairly assume three stories of these 

 complicated frontal convolutions ; the ground floor (a^) rests im- 

 mediately upon the roof of the orbits, whilst the upper story (a^) 

 touches the top of the forehead. In poorly convoluted brains, 

 these windings, viewed from the side, present three distinct 

 superimposed folds ; in richly convoluted brains they appear as 

 closely intertwined plaits, rendering the separation into three 

 stories more difiicult. 



The remarkable differences exhibited by brains are especially 

 shown in these convolutions, above all, in those of the upper 

 and middle (a^) fold. The length of the frontal lobe varies 

 greatly, so that the fissure of Rolando changes its place either 

 in a forward or backward direction. The complication, also, 

 in the shape and arrangement of these convolutions differs, 

 not only in individuals, but even in the two hemispheres of the 

 same brain. The younger Wagner has endeavoured to express 

 these conditions by measuring the surface of the convolutions, 

 and also the development of the furrows separating them. The 

 surfaces were measured by being covered with square pieces of 

 paper four millimeters long, thus covering sixteen square 

 millimeters, — a method evidently much more open to errors 

 than another in which small shps of paper are pressed into the 

 sulci to estimate their depth. 



As it may be assumed, as a general principle, that the extent 

 of subdivision of the frontal lobe gives the measure of the 

 degree of convolution of the whole brain, these measurements 

 have been confined to the frontal lobe and to only a few brains; 

 but they yield important results nevertheless. Assuming the 

 absolute length of all the sulci of the frontal lobe of the brain 

 of the mathematician Gauss := 1 00, we obtain for the brain of 

 Fuchs, the physician, 96 ; for a woman of twenty-nine, about 



