186 A MANUAL OF ANATOMY. 



The Parietal Lobe. Figs. 23, 24, 26. 



Anteriorly the parietal lobe is limited by the fissure of 

 Rolando, posteriorly by the external portion of the parieto- 

 occipital fissure and a line extending in the direction of that 

 fissure, below by the horizontal limb of the fissure of Sylvius 

 and a line continuing its horizontal direction to the posterior 

 boundary. Internally, the parietal lobe merges into the 

 quadrate lobe. For its boundaries see page 191. 



The parietal lobe is furrowed by a single (named) fissure 

 or sulcus, the intraparietal. 



The intraparietal sulcus is usually found in the shape of 

 a horizontal T-shaped groove, the cross-bar of the T being 

 parallel with the fissure of Rolando, and the upright arm 

 with the great longitudinal fissure. This arm is usually 

 prolonged into the occipital lobe, where it serves to mark 

 off the superior from the middle occipital convolutions. 



Between the fissure of Rolando and the transverse arm 

 of the T is the ascending- parietal convolution. This 

 convolution is usually continuous around the lower end 

 of the Rolandic fissure with the ascending frontal convo- 

 lution. The lower ends of these two convolutions together 

 with the adjacent portion of the inferior frontal convolution 

 are called the operculum or roof because they cover in 

 the central lobe or island of Reil. 



The ascending frontal and parietal convolutions are also 

 often united around the upper end of the fissure of Rolando 

 by the paracentral convolution. 



Above the upright arm of the T lies the superior parietal 

 convolution, which is merged into the quadrate lobe on the 

 inner surface of the hemisphere, and below this arm is the 

 inferior parietal convolution, which is further subdivided 

 into two convolutions the anterior one, the supramargi- 

 nal, which arches over the upturned extremity of the hori- 



