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THE FORE-BRAIN OR PROSENCEPHALON 823 



occipital ramus, on to the occipital lobe, where it divides into two parts, which form 

 nearly a right angle with the main stem and constitute the transverse occipital sulcus. 

 The part of the parietal lobe above the horizontal portion of the intraparietal 

 sulcus is named the superior parietal lobule; the part below, the inferior parietal lobule. 



The posterior central gyrus (gyrus centralis posterior; ascending parietal convolution; 

 postcentral gyre) extends from the longitudinal fissure above to the posterior ramus 

 the lateral fissure below. It lies parallel with the anterior central gyrus, with 



hich it is connected below, and also, sometimes, above, the central sulcus. 



The superior parietal lobule (lobulus parietalis superior} is bounded in front by 

 the upper part of the postcentral sulcus, but is usually connected with the pos- 



rior central gyrus above the end of the sulcus; behind it is the lateral part of 



e parietooccipital fissure, around the end of which it is joined to the occipital 

 lobe by a curved gyrus, the arcus parietobccipitalis ; below, it is separated from the 

 inferior parietal lobule by the horizontal portion of the intraparietal sulcus. 



The inferior parietal lobule (lobulus parietalis inferior; subparietal district or lobule) 

 lies below the horizontal portion of the intraparietal sulcus, and behind the lower 

 part of the postcentral sulcus. It is divided from before backward into two gyri. 

 One, the supramarginal, arches over the upturned end of the lateral fissure; it is 

 continuous in front with the postcentral gyrus, and behind with the superior tem- 

 poral gyrus. The second, the angular, arches over the posterior end of the superior 

 temporal sulcus, behind which it is continuous w T ith the middle temporal gyrus. 



The medial surface of the parietal lobe (Fig. 727) is bounded behind by the 

 medial part of the parietooccipital fissure; in front, by the posterior end of the cin- 

 gulate sulcus; and below, it is separated from the cingulate gyrus by the subparietal 

 sulcus. It is of small size, and consists of a square-shaped convolution, which is 

 termed the precuneus or quadrate lobe. 



Occipital Lobe (lobus occipitalis) . The occipital lobe is small and pyramidal 

 in shape; it presents three surfaces: lateral, medial, and tentorial. 



The lateral surface is limited in front by the lateral part of the parietooccipital 

 fissure, and by a line carried from the end of this fissure to the preoccipital notch; 

 it is traversed by the transverse occipital and the lateral occipital sulci. The 

 transverse occipital sulcus is continuous with the posterior end of the occipital 

 ramus of the intraparietal sulcus, and runs across the upper part of the lobe, a 

 short distance behind the parietooccipital fissure. The lateral occipital sulcus 

 extends from behind forward, and divides the lateral surface of the occipital lobe 

 into a superior and an inferior gyrus, which are continuous in front with the parietal 

 and temporal lobes. 1 



The medial surface of the occipital lobe is bounded in front by the medial part 

 of the parietooccipital fissure, and is traversed by the calcarine fissure, which 

 subdivides it into the cuneus and the lingual gyrus. The cuneus is a wedge-shaped 

 area between the calcarine fissure and the medial part of the parietooccipital 

 fissure. The lingual gyrus lies between the calcarine fissure and the posterior part 

 of the collateral fissure; behind, it reaches the occipital pole; in front, it is con- 

 tinued on to the tentorial surface of the temporal lobe, and joins the hippocampal 

 gyrus. 



The tentorial surface of the occipital lobe is limited in front by an imaginary 

 transverse line through the preoccipital notch, and consists of the posterior part 

 of the fusiform gyrus (occipitotemporal convolution) and the lower part of the lingual 

 gyrus, which are separated from each other by the posterior segment of the 

 collateral fissure. 



Temporal Lobe (lobus temporalis}. The temporal lobe presents superior, lateral, 

 and inferior surfaces. 





1 Ellioc Smith has named the lateral occipital sulcus the sulcus lunatus; he regards it as the representative, in the 

 human brain, of the " Affenspalte " of the brain of the ape. 



