340 MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



Spitzka. as quoted by Clever, 1 contributes to the nomenclature and general 

 aspects of the insula. He objects, and I consider his objection well sustained, to 

 naming the shallow groove of a turtle's or serpent's brain, island or fossa although 

 homologous with the insula, and applies the term " fovea centralis" to the con- 

 dition as found in birds and reptiles, " fossa centralis" for its further development 

 in Rodetitia, Insectivora and Marsupialia, and "lobus centralis" where the surround- 

 ing convolutions overlap the retracted area. 



Pansch considers that in Cheiromys we have no fossa Sylvii in the same sense 

 as in the apes ; that is, no island covered by an overgrowing mantle. In any 

 case this formation is very different from what it is in the apes, and is closely 

 connected with the development of the olfactory lobes lying opposite it. In 

 Cheiromys the development takes place in the same manner as in the Carnivora. 

 no overgrowing of the hemisphere taking place, and he believes from these facts 

 that Cheiromys belongs to a separate group from the Primates, which is princi- 

 pally constituted by Carnivores, to which, however, perhaps all other Mammals 

 with furrowed brains may be referred. 



In the Simiadee the insula is as a rule perfectly smooth. In Cynocephalus 

 I found it divided into two equal parts by a deep and well marked furrow, 

 running from its anterior extremity backward a distance of nearly half an inch. 

 In Ateles there were indications of two slight diverging furrows. 



A brief resume will now be given of the relations and conclusions respecting 

 the morphological type of convolutional configuration in the Primates which the 

 writer has adopted as the result of his observations and comparisons. 



GENERAL CONCLUSIONS. 



From the results of my observations I believe that all of the fissures of the 

 hemisphere may be divided into five classes: — 



1. Fundamental primary or typical fissures. 



2. Secondary fissures; those giving special character to the type of convolu- 

 tional configuration. 



3. Vegetative repetitions of the secondary fissures, which increase the 

 complexity of the cerebral surface and which may be termed sulci. 



4. Sulculi ; which give special characteristics to particular groups of brains 

 and are usually repetitions of sulci, or small and apparently irregular fissures. 



5. Rami ; constant branches of fissures or sulci. 



The fundamental or plan fissures are few and simple and constitute the 

 scaffolding or plan around which the secondary type fissures are arranged, bearing 

 precise and symmetrical relations to them, and to the structure of the hemisphere 

 itself. They include in the Primates : 



1. The fissura Sylvii. 



1 Journal of Nervous and Mental Diseases, July, 1879. 



