THE CEREBRUM 



perfectly separated from the gyrus cinguli by a somewhat 

 variable siricus called the sub-parietal sulcus (Fig. 187). 



Lateral Surface of the Parietal Lobe. The gyri and 

 sulci on the lateral surface of the parietal lobe are the 

 following : 



Posterior central. 

 Superior parietal lobule. 

 Gyri-f Inferior ( Supra-marginal. 



parietal^ Angular. 

 \Jobule. [Postparietal. 



I Sulcus postcentralis 

 inferior. 

 Sulcus postcentralis 

 superior. 

 Ramus horizontalis. 

 Ramus occipitalis. 

 Upturned ends of 



(a) Posterior branch of 



lateral. 



(b) Superior temporal. 



(c) Middle temporal. 



Interparietal Sulcus of Turner. This is a composite 

 sulcus built up of four originally distinct factors. Two of 

 these, termed the sulcus postcentralis inferior and the sulcus 

 postcentralis superior, take a more or less vertical course 

 across the hemisphere, and are frequently continuous with 

 each other. The other two factors are placed horizontally, 

 one posterior to the other, and they are called the ramus 

 horizontalis and the ramus occipitalis. 



The sulcus postcentralis inferior lies posterior to the lower 

 part of the central sulcus (O.T. Rolando), whilst the sulcus 

 postcentralis superior occupies a similar position in relation 

 to the upper part of that sulcus. When confluent with each 

 other they form a long continuous furrow, which stretches 

 across the hemisphere, posterior and parallel to the central 

 sulcus (Fig. 1 86). 



The ramus horizontalis (Fig. 186) is continuous with the 

 upper end of the sulcus postcentralis inferior, and extends 

 posteriorly, with a slight inclination upwards, between the 

 superior parietal lobule above and the inferior parietal lobule 

 below. With the two confluent postcentral sulci it presents a 

 figure like the letter | placed on its side. 



The ramus occipitalis (Fig. 186) is a curved sulcus. It 

 forms the lateral boundary of the arcus parieto-occipitalis, 

 which surrounds the lateral part of the parieto-occipital fissure. 

 Sometimes the ramus occipitalis is linked on to the ramus 

 horizontalis more frequently it is separate. Its posterior 

 end runs into the occipital lobe, and, posterior to the arcus 



