CEREBRUM. 409 



to the base, while the lateral surfaces are also a little flat- 

 tened. All the surfaces of the cerebrum are marked by 

 distinct eminences, which, from their turnings and resem- 

 blance to the intestines, are called convolutions, (Fig. 115, 

 A,) while the deep furrows every where seen separating the 

 convolutions are named anfractuosities , and range from a 

 quarter to an inch and a half in depth. 



The surface of the convolutions presents a smooth and 

 polished appearance, from the presence and covering of the 

 arachnoid membrane. " A convolution is defined to be a 

 convex fold of superficial gray neurine, covered all round 

 to its base by pia mater ; and a sulcus is a depression or in- 

 volution between any two or more convolutions, and lined 

 by a continuation of the gray lamina." 



The convolutions are very varied, both in their form and 

 number, and though seemingly on first view distinct, yet 

 they really are continuous with and run into each other, 

 though there is nevertheless a close, if not a perfect sym- 

 metry between those of opposite sides. 



These convolutions constituting the cortical portion, are 

 called by Mr. Solly the hemispherical ganglia, and their 

 structure does not consist, he says, of a single layer of gray 

 or cortical matter, but according to the microscopic obser- 



FIG. 115. A 



vations of M. Baillarger, of six layers, three layers of 

 the gray, alternating with three of the white, (Fig. 115, B.) 

 Counting from within, the first is represented as gray, the 



FIG. 115, A represents the convolutions of one side of the cerebrum, a An- 

 terior lobe of cerebrum. 6 Posterior lobe, c Middle lobe. 



FIG. 115, B represents the six alternate layers of gray and white neurine, 

 composing a convolution of the human brain. 



