THE CEREBRUM 323 



fissure, in part, and rests on the orbital plate of the frontal 

 bone. The gyres are the precentral, superfrontal, medifrontal, 

 and subfrontal. The fissures are the precentral, superfrontal, 

 and subfrontal. The orbital surface of the frontal lobe is marked 

 by the olfactory fissure, which lodges the olfactory bulb and 

 tract, and separates the mesorbital gyre from the preorbital 

 and postorbital gyre fields. The latter are subdivided by the 

 transorbital fissure. Sometimes the postorbital limbus may 

 be seen on this surface. It consists of a curved, welt-shaped 

 eminence demarcated by an incisure created by the lesser 

 wing of the sphenoid, and due, apparently, to the intrusion 

 of the postorbital portion into the middle fossa of the skull. 

 (Gray.) 



The mesal surface of the frontal lobe presents the paracentral 

 gyre, limited by the caudal and cephalic limbs of the paracentral 

 fissure; the superfrontal and callosal gyre, separated by the 

 supercallosal fissure and the rostral fissure is found in the 

 inferior region of this surface. 



The parietal lobe, lateral surface, is bounded in front by the 

 central fissure, below by the Sylvian fissure, above by the 

 dorsimesal border; it is only partially separated from the occipital 

 lobe by the occipital fissure, merging gradually into the tem- 

 poral lobe. The gyres are the postcentral, the parietal, the 

 subparietal the marginal, the angular, the postparietal ; the 

 paraoccipital is the gyre connecting the parietal and occipital 

 gyres. The marginal connects the postcentral and super- 

 temporal gyres; the angular connects the supertemporal and 

 meditemporal gyres. The fissures are the postcentral, the 

 subcentral, the parietal; the paraoccipital (anterior portion). 

 The less constant fissures are the transparietal and the inter- 

 mediate fissures. In the subparietal region terminate the 

 upturned ends of the Sylvian (i. e., episylvian ramus), and the 

 supertemporal and meditemporal fissures. 



The mesal surface of the parietal lobe. The precuneus 

 gyre is found, separated in front and above from the paracentral 

 gyre by the paracentral fissure, below and above, from the cuneus 

 by the occipital fissure; w r hile below and in front it is demar- 

 cated from the callosal gyre by the precuneal fissure. 



The occipital lobe, the lateral surface is bounded anteriorly 

 by the occipital fissure, which partially separates it from the 



