202 C. W. M. POYNTER AND J. J. KEEGAN 
elements of the sulcus. The third element is the deepest and 
most prominent of the three. In the great majority of cases it 
crosses the border of the hemisphere and communicates with the 
sulcus temporo-parietalis as already noted. 
The sulcus cinguli has a very constant form in this series of 
hemispheres; Eberstaller’s classification into three elements may 
be followed for the purpose of description but does not corre- 
spond to the conditions here presented. The greatest irregular- 
ity occurs in the anterior region, where it is often impossible to 
distinguish between a pars anterior and a sulcus rostralis or sul- 
cus fronto-marginalis (fig. 6). The only point at which a 
definite division of the sulcus cinguli can be made out is at the 
junction of the anterior two-thirds and the posterior third. The 
pars posterior has a very inconstant form and is frequently 
represented, as in figure 6, by two or three diagonal elements. 
The incisura cinguli appears to be the most constant feature 
of the complex. It has the superficial appearance of a continu- 
ation of the pars posterior sulcus cinguli across the mesial border 
of the hemisphere; an examination of the floor of the sulcus, 
however, reveals a condition somewhat comparable to that 
found in the fossa parieto-occipitalis. There appears to be a 
division in the depth of the sulcus which encloses a raised portion 
of cortex. The posterior branch of this division is the direct 
continuation of the sulcus proper and ends within the incisura. 
The lateral branch continues over the border and constitutes 
the ‘paracentral sulcus.’ The atypical cases of incisura are 
simply a wide separation of these two elements. 
The lobulus precuneus does not present a regular form of 
fissuration. A more or less horizontal suleus subparietalis is 
always present. The sulcus precuneus is represented by two or 
more elements, one of which cuts across the mesial border of the 
hemisphere in the majority of cases and forms an incising sulcus 
of the gyrus arcuatus medius of the lobulus parietalis superior. 
The marked operculation over the gyrus intercuneatus has 
already been noted. 
The fossa parieto-occipitalis conforms in general to the de- 
scription of Elliot Smith. The inferior portion of the fossa 
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