THE CEREBRAL HEMISPHERES 



923 



2. Mfftal Surface. On the mesal surface of the frontal lobe and embracing 

 the dorsal end of the central fissure lies an oval lobule or gyre called the paracentral 

 gyre (lohnliix paracentralis), limited by the paracentral fissure with its caudal 

 and cephalic limbs. Frontad thereof extends the large arched mesal surface of 

 the superfrontal gyre (gyrux froutalis superior}, limited by the supercallosal fissure. 

 Between the latter fissure and the callosal fissure, concentrically situated with 

 respect to the superfrontal, lies the callosal gyre (the "gyrus fornicatus" of other 

 authors). 



Frontad these two gyres arch around the genu of the corpus callosum, to become 

 merged through the disappearance of the intervening supercallosal fissure, and the 

 rostral fissures alone mark this surface. 



INTERCEREBRAL F. 



F. = FISSURE 

 . = GYRE 



FIG. 676. Fissures and gyres of the basal surface of the cerebrum. 



3. Orbital Surface. The olfactory fissure and the mesorbital border hound 

 the mesorbital gyre (gyrus rectus). The remaining orbital surface is not regularly 

 divisible on account of the great variability of the orbital fissures; when the trans- 

 orbital fissure is pronounced, a pre- and postorbital gyre may be distinguished. 



The postorbital limbus is a formation occasionally met with on the orbital sur- 

 face. 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. 



II. Parietal Lobe (lobus parietal is}. FISSURES OF THE PARIETAL LOBE. 1. 

 The lateral surface is bounded by the dorsimesal border, by the central fissure, 

 and by a part of the sylvian fissure; it is only partially demarcated from the 

 occipital lobe by the occipital fissure, and merges gradually into the temporal 

 lobe. 



