470 THE BRAIN 



sulcus which receives the name of gyrus orbitalis medialis. 

 The transverse limb takes a curved course with the concavity 

 directed posteriorly. It divides the district between the 

 lateral and medial limbs into an anterior part, or gyrus orbitalis 

 anterior, and a posterior part, or gyrus orbitalis posterior. The 

 latter corresponds with the greater part of the orbital oper- 

 culum. 



Boundaries of the Parietal Lobe. The parietal lobe forms 

 a considerable part of the lateral surface of the cerebral hemi- 

 sphere, and it appears also on the medial face, where it forms 

 the prsecuneus and the posterior part of the paracentral 

 lobule. Anteriorly, it is bounded by the central sulcus, 

 which separates it from the frontal lobe. Below, it is 

 bounded in the anterior part of its extent by the posterior 

 branch of the lateral fissure. Posterior to the upturned end 

 of that fissure, it is quite continuous inferiorly with the 

 temporal lobe, and an arbitrary line drawn posteriorly on the 

 surface of the brain in continuation of the posterior branch 

 of the lateral fissure is taken as its inferior limit (Fig. 186). 

 Posteriorly, it is separated from the occipital lobe, at the supero- 

 medial border of the hemisphere, by the lateral part of the 

 parieto-occipital fissure. Below that it is more or less directly 

 continuous with the occipital lobe, but an arbitrary line 

 drawn across the lateral surface of the hemisphere from the 

 extremity of the parieto-occipital fissure to an indentation 

 on the infero-lateral border of the hemisphere, termed the 

 pra-occipital notch, may be regarded as furnishing a posterior 

 limitation. The prae-occipital notch is, as a rule, visible only 

 in brains that have been hardened in situ. It is produced 

 by a slight wrinkle or fold of the dura mater, on the deep 

 aspect of the parieto-mastoid suture and in relation to the 

 portion of the lateral venous sinus which lies in this locality. 

 The notch is placed on the infero-lateral border of the hemi- 

 sphere, about one inch and a half anterior to the occipital 

 pole. 



Medial Surface of the Parietal Lobe Prsecuneus and 

 Posterior Part of Paracentral Lobule. On the medial 

 surface of the hemisphere the parietal lobe is represented 

 by the pracuneus and the posterior part of the paracentral 

 lobule. This district, which is somewhat quadrilateral in form, 

 lies between the upper end of the central sulcus and the 

 medial part of the parieto-occipital fissure. Below, it is im- 



