THE BRAIN 131 



eminentia collateralis in the descending cornu of the lateral 

 ventricle. 



6. Limiting sulcus of Reil, round the island of Reil (p. 133). 



THE LOBES. 



The hemispheres are by the above fissures arbitrarily 

 divided into seven lobes, viz. : 



1. Frontal: limited below by the Sylvian fissure, behind by 

 the fissure of Rolando, internally by calloso-marginal fissure. 



2. Parietal: limited in front by the fissure of Rolando, and 

 behind by the parieto-occipital fissure ; below by fissure of 

 Sylvius continued backwards, and internally by calloso- 

 marginal fissure. 



3. Occipital: Bounded in front by the parieto-occipitai 

 fissure ; forms the posterior part of the hemisphere. 



4. Temporo-sphenoidal : occupies middle fossa at the base of 

 the skull, being placed behind the Sylvian fissure, and below 

 the parietal and occipital lobes, internally separated from 

 limbic lobe by collateral fissure. 



5. Central or Island of Reil: contained in the Sylvian fissure ; 

 triangular in shape. 



6. Limbic or falciform: consists of caliosal and uncinate 

 gyri, bounded above and in front by calloso-marginal and 

 below by collateral fissures. 



7. Olfactory : lying on the under surface of the frontal lobe, 

 sometimes termed the olfactory nerve. 



The frontal lobe : 

 Convolutions and sidci : 

 On Tinder surface : 



The tri-radiate or orbital sulcus divides this surface 

 into an inner, anterior, and posterior or outer orbital 

 convolutions. On the inner convolution is the olfactory 

 sulcus, which contains the olfactory lobe. 

 On outer surface : 



The ascending frontal or precentral convolution is bounded 

 behind by the fissure of Rolando, round the lower end 

 of which it joins the ascending parietal convolution ; 

 in front by the precentral sulcus. 



The longitudinal frontal convolutions are three in 

 number, upper, middle, and inferior ; they occupy the 

 rest of the outer surface and are separated from each 

 other by two sulci, and from the ascending convolution 

 by the precentral sulcus. 

 On itmer surface : 



The marginal convolution extends along the edge of the 

 longitudinal fissure. It commences at the anterior 



7 



