192 A MANUAL OF ANATOMY. 



The first part of this arch is called the gyrus fornicatus, 

 the second part the uncinate gyrus ; they are connected by 

 a narrowed portion :the isthmus just under the posterior 

 part of the corpus callosum. Together these convolu- 

 tions, with some internal parts, as the septum lucidum, 

 fascia dentata, and fornix, constitute the falciform or limbic 

 lobe. 



The uncinate convolution is the anterior part of the 

 superior occipitotemporal convolution, which lies between 

 the calcarine and the collateral fissures. 



The posterior part of this convolution is also called the 

 Ungulate convolution. 



External to the collateral fissure, between it and the 

 inferior temporal sulcus, is the inferior, or simply the oc- 

 cipitotemporal, convolution. Some writers call the por- 

 tion of the falciform lobe which lies behind and below the 

 hinder end of the corpus callosum the gyrus hippocampi, 

 restricting the uncinate gyrus to the anterior part of the 

 hook. 



The dentate convolution will be seen best during the dis- 

 section. This is the thin fold which passes from the end 

 of the corpus callosum to the apex of the temporal lobe. 

 It is found within the arch of the uncinate gyrus. 



The Callosal Sulcus. Figs. 27, 38. 



This is the groove which is found between the corpus 

 callosum and the gyrus fornicatus. 



The Base of the Brain. Figs. 28, 29. 



The Sulci and Convolutions. The under surface of the 

 frontal lobe : Here are found two shallow sulci, an external 

 one shaped something like the letter H or X. This is the 

 orbital sulcus, and the convolutions formed by it are the 

 internal, anterior, and the posterior or external. 



