THE CEREBRAL HEMISPHERES 925 



supertemporal and meditemporal gyres. The postparietal gyre is not always 

 clearly defined; it arches around the upturned end of the meditemporal or its 

 representative segment; mesally it is bounded by the paroccipital fissure. Variable 

 intermedial fissures sometimes help to define the angular gyre from its two neigh- 

 bors. 



2. The mcxal surface of the parietal lobe has already been described as equiva- 

 lent to the precuneus, from its position in "front" of the cuneus or quadrate lobe 

 from its general shape. It is sometimes marked by a mesal extension of the 

 transparietal fissure or by intraprecuneal fissures. 



III. Occipital Lobe (lobus occipitalis). FISSURES OF THE OCCIPITAL LOBE. 

 1. The lateral surface of the occipital lobe is imperfectly demarcated from the 

 adjacent parietal and temporal lobes in most brains. The sharply defined 

 exoccipital fissure or " Affenspalte" of other primates has, in the ancestry of man, 

 been reduced to a series of fissural segments by the upgrowth of submerged cor- 

 tical parts. The paroccipital fissure, we have already learned, probably repre- 

 sents one of the gaps in the series; another may be the sulcus lunatus (Elliott 

 Smith), usually termed the lateral occipital by the authors; lastly, a fissure some- 

 times called the inferior occipital (suboccipital), and usually embraced, on the 

 occipital pole, by the bifurcate limbs of the postcalcarine, may complete the series. 

 Further researches are necessary to elucidate the morphology of this region. 



2. The mesal surface is equivalent to the wedge-shaped region embraced by 

 the occipital and calcarine fissures, and called the cuneus. A fairly constant 

 cuneal fissure traverses its surface parallel to the calcarine. 



If it is ever determined that the morphological boundary of the occipital lobe is 

 as outlined above, the lobe is practically excluded from the basal surface of the 

 hemicerebrum. 



IV. Temporal Lobe (lobus temporalis}. FISSURES OF THE TEMPORAL LOBE. 1. 

 The lateral surface of the temporal lobe is bounded by the basisylvian and sylvian 

 fissures and by the ventrolateral border; caudally it merges into the adjacent 

 parietal and occipital lobes. 



The supertemporal fissure (sulcus temporalis superior) is a deep, long (10 to 12 

 cm.), and usually continuous fissure which begins near the temporal pole, proceeds 

 ventrad of but parallel with the sylvian, to become upturned in the parietal lobe 

 and embraced by the arched angular gyre. 



The meditemporal fissure (sulcus temporalis medius) is rarely continuous; more 

 often it is represented by a series of segments, two, three, or four in number, the 

 caudal segment running more vertically into the parietal lobe to be embraced by 

 the postparietal gyre. The meditemporal fissural segments run nearly parallel 

 with the supertemporal and demarcate the meditemporal from the subtemporal 

 gyre. 



2. Tentorial or Ventral Surface. Close to the ventrolateral margin and more 

 or less parallel with it runs the subtemporal fissure (sulcus temporalis inferior), 

 extending from near the temporal to near the occipital pole. It is rarely continu- 

 ous, being usually broken up into two or more segments. It demarcates the sub- 

 temporal from the subcollateral gyre. 



The collateral fissure (fissura collateralis] is a well-marked, long (8 to 12 cm.), and 

 deep fissure extending from near the occipital to near the temporal pole. Caudally 

 it demarcates the subcalcarine gyre from the subcollateral; frontad it intervenes 

 between the latter gyre and the hippocampal gyre. Its middle part is correlative 

 with the collateral eminence. On the ventromesal aspect of the temporal lobe 

 and near its pole, cephalad of the uncus, is a moderately marked fissure or groove, 

 called, because of its topographic relation to the amygdaline nucleus a gray, 

 ganglionic mass the amygdaline fissure (fissura ectorhinalis s. postrhinalis), or 

 incisura temporalis. 



