Literary Notices. xi 



14. The union between these two elements of the sulcus, as 

 Ecker and Wilder have shown, is much more common on the left side 

 than on the right. 



The sulcus transversus of Ecker is not the homologue of the "Af- 

 fenspalter" in the apes, but merely a terminal bifurcation of the ramus 

 occipitalis." 



The Sulcus Priscentralis. 



1 . The sulcus praecentralis inferior in the human brain is com- 

 posed of a vertical and a horizontal limb. The latter is carried for- 

 wards into the middle of the frontal convolution. 



2. This furrow is the earliest to appear on the outer surface of 

 the frontal lobe of the foetal brain. In some cases it is seen in the 

 fifth month cerebrum in the form of a long, deep, vertical sulcus, 

 which subsequently undergoes a retrograde development before its 

 adult condition is reached. In many cases, in its early condition, it 

 presents a form in every respect comparable with that observed in the 

 cerebrum of the low ape (Cebas.) Frequently it is developed in 

 several pieces. 



3. The sulcus prsecentralis superior is closely connected with 

 the basal part of the first frontal furrow. It is usually developed 

 along with it. It consists of two pieces — an upper and a lower — 

 which may be partially or completely separated from each other, as 

 well as from the basal part of the first frontal furrow by an annectant 

 gyrus. 



4. Two additional furrows belongmg to the praecentral system 

 are occasionally present, viz : the sulcus praecentralis medius and the 

 sulcus praecentralis marginalis. 



5. The sulcus praecentralis medius may arise in two different 

 ways : (a) it may be formed by the ramus horizontalis of the inferior 

 praecentral sulcus divorced from the vertical stem and assuming a 

 very oblique or an almost vertical position : {b) It may consist of a 

 new element placed between the superior and inferior praecentral 

 furrows, but showing a closer connection with the former." * * * 



"12. The superior frontal gyrus and the middle frontal gyrus are 

 each partially subdivided into two tiers or subdivisions by furrows 

 which may be respectively termed the sulcus frontalis mesialis and the 

 sulcus frontalis medius. 



13. Both of these furrows have secured a firm footing in the hu- 

 man brain, but only one (viz., the frontalis medius) has established it- 

 self upon the brain of the chimpanzee." * * * 



