38 C. JJ'. M. Poynter 



to the principal sulcus of anthropoidae. He considered the sulcus 

 centralis, which limits the posterior insula anteriorly, as a forma- 

 tion almost exclusively human. He saw two types of human 

 development in the posterior insula, one belonging to low apes, 

 and one to anthropoids. He attempted to interpret any fissure 

 remnant according to these types as belonging to the central or 

 longitudinal sulcus. 



Sergi (1910) considers that Holl has carried the homology 

 farther than the region in its simplicity warrants. The homology 

 in the posterior insula is represented by the necessity of a longi- 

 tudinal sulcutura. not by the specification of any sulcus segment. 

 He agrees with Holl in dividing the insular cortex into two areas 

 divided by the sulcus centralis insulae, and this agrees with the 

 findings of Flechsig. Campell and others. 



Sergi (1910) finds from a study of the more primitive races 

 that the posterior portion of the insula is more stable than the 

 anterior, although a unique type of sulcus arrrangement does not 

 exist for man. Generally two zones can be distinguished, though 

 one or the other may be greatly displaced. A'ariations between the 

 two insulae of a brain do not obey a common law, yet there gener- 

 ally exists a similarity in sulci segments and their connections. 

 Sergi concludes that there are no determinable ethnological or 

 sex distinctions in the insula. 



Although we cannot establish a type of sulcus arrangement for 

 man, we can recognize in a complex development two separate 

 zones, one made up of five g>ri and the other of two gyri. \'aria- 

 tions in the anterior zone will depend on the lack of some one or 

 more of the sulci brczcs. In the posterior zone variations will 

 depend on the presence or- absence of the segments making up 

 the sulcus centralis and the sulcus longitudinalis and their anas- 

 tomoses. Holl and Sergi have shown that either the sulcus cen- 

 tralis or longitudinalis may be absent in part or completely, and 

 if one segment be present, it may be independent or in connection 

 with the other sulcus. Also the sulci breves are not infrequently 

 confluent with the sulcus centralis or its segments. In the light of 

 these variations, Weinberg's ( 1906) report of an interruption of 

 the sulcus centralis insulae loses its significance. Giacomini 



^82 



