36 C. W. M. Poynter 



parallel to the mesial border. Smith (19046) is not sure that the 

 fissure is the same as the sulcus saggitalis (Retzius), or the post- 

 cuneal fissure (Wilder), but points out that both names are in- 

 correct because of the usual position of the sulcus on the dorsal 

 surface of the region. 



The Sulcus Occipitalis Inferior: This sulcus is subject to great 

 variations in position, shape and number of segments. It may be 

 impossible to identify because of its fusion with the sulcus 

 temporalis medius. 



The Sulcus Occipitalis Superior: This sulcus is less constant 

 than the inferior, Smith suggests, because it is being pushed onto 

 the mesial surface. He says, " It often happens in the human 

 brain that the homologue of the ' Y' shaped sulcus of apes retains 

 the same position relative to the whole striate area as in apes, i. e., 

 the ' Y ' shaped caudal end is swept far onto the mesial surface." 



LOBUS INSULARIS 



While the insula was probably recognized by Vicq d'Ayzer and 

 described by Reil (1804), it was not clearly presented till Holl 

 (1908-9) and Sergi (1910) published their excellent memoirs. 

 All authors are agreed in dividing the insula into two cortical 

 areas by a principal sulcus, called the sulcus centralis insulae. 

 Holl called these cortical areas, so divided, the anterior superficial 

 and posterior deep portions of the insula. The anterior portion 

 is on a plane with the orbital surface, and is bounded by the sulcus 

 marginalis anterior, the homologue of which Marchand (1893) 

 declared was the sulcus fronto-orbitalis of anthropoids. It is 

 triangular in shape and is divided into gyri, typically three (Holl), 

 more or less converging and having a common root. The sulci in 

 this part are for the most part short and vary in number and 

 orientation. Sergi calls them sulci breves insulae and has found 

 them frequently arranged radiating from a common point in a fan 

 formation (conformazione a ventaglio). 



The posterior, or posterior inferior portion, forms a covered 

 convolution situated in the floor of the Sylvian fossa, which 

 begins below on the orbital surface, and extends postero-supe- 

 riorly along the upper surface of the temporal lobe. It is sepa- 



380 



