40 



C. W. M. Poxnter 



temporalis transversus superior. There is also occasionally a 

 communication between the sulcus temporalis superior and the 

 fissura Sylvii which he figures but for which he has not given the 

 per cent. He speaks of the division of the sulcus into two seg- 

 ments (29 per cent.). Duckworth finds the same condition in 

 31 per cent, for embryos. 



The Sulcus Temporalis Medius: This sulcus has not received a 

 careful study at the hands of observers. It is generally repre- 

 sented not by a single sulcus, but by two or three segments which 

 may be an advance over the Simiidae. The sulcus temporalis will 

 be discussed with the inferior surface. 



REGIONES MEDIA ET INFERIOR 



Lohus frontalis. 



On the antero-inferior surface of this region are a group of 

 three sulci which are very inconstant. The sulcus rosfralis is 

 most important in size and constancy ; it may be represented by 

 two or three small segments or it may be a single long fissure 

 running parallel to the anterior portion of the sulcus cinguli. It 

 may communicate with either of the other fissures of the group 

 or with the sulcus cinguli. The sulcus rostralis transi'crsus and 

 sulcus rostralis inferior are small inconstant fissures represented, 

 when present, by few segments and not infrequently establishing 

 the connections just referred to. 



The Sulcus Cinguli: This is the principal sulcus of the region. 

 Eberstaller (1900) recognized three elements in its make up, 

 viz., a pars anterior, a pars intermedia, and a pars posterior. The 

 connections and development of these elements largely represent 

 the variations found in this sulcus. Retzius (1896) found that 

 the sulcus was in two parts in 44 per cent., and in three parts in 

 14 per cent. He noticed an additional variation which he termed 

 a doubling of the pars anterior and which he said was of not in- 

 frequent occurrence. Weinberg (1905) found a continuous 

 sulcus in 54 per cent., in three parts in 10 per cent., and pars 

 anterior separate; the other two joined in 32 per cent. 



Lohus Parietalis. (Praecuncus.) 



The variations of fissure arrangement in this region are very 



384 



