16 BEAN. 



These three fissures divide the brain into lobes. 



1. Above the lateral fissure and in front of that of Rolando, the frontal lobes. 



2. Above the lateral fissure and between that of Rolando and a line prolonging 

 the occipito-parietal fissure on the outer surface of the brain, the parietal lobes. 



3. Behind this line and the occipitoparietal fissure, the occipital lobes. 



4. Below the lateral fissure, the temporal lobes. 



(These lobes are merely topographical divisions. They have no special physio- 

 logic or morphologic significance.) 



In the frontal lobe, on the outer surface note : 



1. Parallel to the fissure of Rolando, the precentral sulcus usually divided by 

 a small convolution into two parts. 



2. The convolution between this and the fissure of Rolando is the ascending 

 frontal or precentral convolution. 



3 and 4. The superior and inferior frontal sulci extend tangentially forward 

 from the precentral sulcus. They are somewhat irregular in their course. These 

 divide the anterior part of the frontal lobe into: 



5. 6, and 7. The superior, middle, and inferior or 1st, 2d, and 3d frontal 

 convolutions. 



8 and 9. Two arms pass upward from near the beginning of the lateral 

 fissure; these are the ascending and anterior horizontal limbs of the lateral fissure 

 forming the three opercula 10, 11, and 12, fronto-parietal, frontal, and orbital. 



Elevate the opercula and examine the long and short convolutions of the island 

 and the circular sulcus of Reil. 



On the inner surface of the frontal lobe: 



1. The sulcus of the corpus callosum is immediately above the corpus callosum. 



2. Above this the fornicate convolution. 



3. Above this the sulcus of the cingulum. 



4. Above this the marginal convolution. 



Note that behind, the sulcus of the cingulum bends upward to meet the upper 

 edge of the brain, and that the upper end of the fissure of Rolando is 1 to 2 

 centimeters in front of the point where the sulcus of the cingulum reaches the 

 edge. 



5. Note a fissure coming down from the edge of the brain about 3 centimeters 

 or more in front of the upturned portion of the sulcus of the cingulum. This 

 cuts off the hinder portion of the marginal gyrus, known as the paracentral lobule. 



The sulci and convolutions on the orbital surface of the frontal lobe form an 

 H with the gyrus rectus mesial to it. 



On the outer surface of the paracentral lobule : 



1. The postcentral sulcus is parallel with the fissure of Rolando. 



2. Between Rolando and the postcentral sulcus is the ascending parietal or 

 postcentral convolution. 



3. Running backward horizontally from the postcentral sulcus is the inter- 

 parietal sulcus. 



4. Below this, and ascending round the posterior end of the lateral fissure is 

 the supra-marginal convolution. 



5. Below 3 and behind 4 and arching around the posterior end of the first 

 temporal sulcus (t. e., the first sulcus below the lateral fissure) is the angular 

 convolution. 



On the inner surface of the parietal lobe: 



1. A quadrangular area between the upturned portion of the sulcus of the 

 cingulum and the parietooccipital fissure, the quadrate lobe or precuneus. 



On the inner surface of the occipital lobe: 



1. The calcarine fissure running from behind forward, joining the lower end 

 of the occipito-parietal and then being continued forward on the under surface 

 of the temporal lobe. 



