146 THE CEREBRAL HEMISPHERES. 



occasionally runs into the calloso-marginal, to which it has sometimes been regarded 

 as belonging (Schwalbe '). The next portion (sulcus precentralis superior), is very 

 often continued forwards into the first frontal sulcus (/ fig. 101). Its middle part is 

 opposite the upper genu of the fissure of Kolando. The inferior portion (sulcus 

 precentralis inferior} is by far the best marked. It separates the ascending frontal 

 from the third frontal gyrus, and usually gives off a well-marked branch anteriorly 

 into the middle frontal gyrus (which may, as in fig. 101, p.c.i.ant., be the main 

 continuation of the fissure). After giving off this branch the fissure is usually pro- 

 longed upwards for some distance, but this is not shown in the brain figured, where 

 the superior precentral extends unusually low down. The inferior precentral sulcus is 

 often joined to the Sylvian fissure, either directly or through the intermediation 

 of the sulcus precentralis transversus (see p. 143), or of the sulcus diagonalis (see 

 p. 148), but there is usually, perhaps invariably, an annectent gyrus concealed in 

 the depth, of .the fissure even in these cases. The inferior frontal sulcus sometimes 

 appears to spring from the inferior precentral, either near its middle, or, as in the 

 brain figured, from its anterior branch, but the two are probably more frequently 

 separated by an annectent gyrus which here joins the middle and inferior frontal gyri. 



Two well-marked sagittal sulci (superior and inferior frontal) course over the 

 external surface of the frontal lobe in front of the precentral fissure ; they subdivide 

 this part of the lobe into three sagittal gyri, superior, middle and inferior. Besides 

 these constant sulci, there are certain others which are less constant in their 

 occurrence, and in the extent to which they are developed as connected fissures, viz., 

 one running along the middle of the superior frontal gyrus, which we will term from 

 its position near the upper border, the paramesial sulcus (fig. 101, / 4 ), (s. mesialis of 

 Cunningham), and one running along the centre of the middle frontal gyrus (sulcus 

 frontalis medius of Eberstaller), (fig. 101,/ 3 ). Both of these are not only inconstant 

 in their occurrence, but when present are frequently interrupted, and then appear to 

 consist of a series of separate parts, which are often united here and there with the 

 other frontal sulci. 



The midfrontal sulcus (s. frontalis medius) usually bifurcates in front, and 

 becomes transverse (s. transversus anterior, frcnto-marginal sulcus of Wernicke). 



The superior frontal sulcus (/i ) is developed after the inferior, and along with 

 the upper part of the precentral, with which it is usually in direct continuity. This 

 sulcus is often interrupted by superficial annectent gyri passing obliquely from before 

 backwards from the first to the second frontal convolution. Anteriorly, the superior 

 frontal often passes into the mid-frontal sulcus (Cunningham). This is the case in 

 the brain figured (fig. 101). Posteriorly, its line may be continued by a branch 

 from the superior precentral sulcus passing across the ascending frontal gyrus. This 

 was also the case in the brain here figured. 



The inferior frontal sulcus (f. 2 ) usually curves forwards from the middle of the 

 inferior precentral sulcus towards the frontal pole of the hemisphere. Several small 

 secondary furrows pass from it above and below, and it is sometimes subdivided by 

 superficial annectent gyri into three portions. Anteriorly it bifurcates, forming a 

 transverse piece, which may develop separately. At the apex of the lobe, in front 

 of and sometimes forming part of this fissure, are one or two transverse sulci 

 forming the sulcus radiatus and lateral fronto-marginal sulcus of Eberstaller. 



Gyri. Four convolutions are described upon this surface, three of which run 

 antero-posteriorly, while the fourth takes a direction obliquely across the brain, and 

 parallel with the fissure of Kolando. The three antero-posterior convolutions are 

 termed respectively the superior, middle and inferior, m first, second, and third frontal 



1 Schwalbe has termed it the "sulcus paracentralis, " but this is not to be confounded with the 

 fissure to which that name has been given by Wilder (p. 145). 



