292 



HUMAN ANATOMY. 



The principal lobes of the brain are six, as follows : 



1. Frontal lobe, on the outer surface of the brain; it is bounded 

 below by the fissure of Sylvius, and behind by the fissure of Rolando. 

 On the mesial surface it is bounded by the callaso-marginal fissure, and 

 on the inferior surface it is bounded behind by the stem of the Sylvian 

 fissure. 



On the outer surface it is divided into the 



(a) Gyrus frontalis ascendens; 



(b) Gyrus frontalis superior; 



(c) Gyrus frontalis medius; 

 (dj Gyrus frontalis inferior. 



SuLM. 



FlS.p-Q, 



Hs.cak. 



PIG. 134. 



Convolutions and fissures of the median and tentorial surfaces of 

 the right cerebral hemisphere. Fis. S., fissure of Sylvius; Sul. cal. 

 marg., calloso-marginal sulcus; Sul. subf., subfrontal sulcus; Sul. 

 C. C., sulcus of corpus callosum; Sul. marg., marginal sulcus; Sul. 

 subp., subparietal sulcus; Fis. p. o., parieto-occipital fissure; Fis. 

 calc., calcarine fissure; Fis. den., dentate fissure; Fis. col., collateral 

 fissure. (After Van Gehuchten.) (Whitchead.) 



On the mesial surface it is divided into 



(a) Gyrus marginalis; 



(b) Paracentral lobule. 



On the orbital surface it is divided into 

 (a) Gyrus orbitalis internus; 

 (bj Gyrus orbitalis anterior; 



(c) Gyrus orbitalis posterior. 



2. Parietal lobe, lies between the fissure of Rolando, the parieto- 

 occipital, and the fissure of Sylvius, and consists of five gyri: 



(a) Ascending parietal; "| Supramarginal, 



(b) Superior parietal; V Angular, 



(c) Inferior parietal, J Post parietal; 



