750 



DISSECTION OF THE BKA1N. 



Orbital 

 sulcus and 

 gyri. 



Olfactory 

 sulcus. 



Parietal 

 sulci are 



intra- 

 parietal, 



which has 

 ascending 

 and hori- 

 zontal parts. 



Orbital lobule (fig. 272). The orbital lobule is subdivided by a Y- 

 or H-shaped orbital sulcus (orb) into three convolutions, named 

 internal (10), anterior (AO), and posterior (PO), orbital, which are the 

 continuation respectively of the superior, middle, and inferior 

 frontal convolutions. On the internal orbital convolution is a longi- 

 tudinal groove olfactory 

 sulcus (ol), for the recep- 

 tion of the olfactory lobe. 



SULCI AND CONVOLU- 

 TIONS OF THE PARIETAL 



LOBE. In the parietal 

 lobe there are two named 

 sulci ; and four convolu- 

 tions are distinguished. 



The intraparietal sulcus 

 (tig. 270, ip) begins close 

 to the posterior branch 

 of the fissure of Sylvius, 

 about midway between 

 the upturned extremity of 

 this and the lower end 

 of the sulcus of Rolando. 

 It first ascends, running 

 nearly parallel to the 

 lower half of the latter 

 sulcus, and then is directed 

 backwards to the hinder 

 limit of the parietal lobe, 

 where it often becomes 

 continuous with the supe- 

 rior occipital sulcus. Com- 

 monly, also, it ends in a 

 forked manner in a sulcus, 

 (anterior occipital), which 

 passes from above down- 

 wards at the front of the 

 occipital lobe. The upper, 

 or horizontal, part of the 

 intraparietal sulcus is fre- 

 quently interrupted by 

 one or two cross gyri. 

 The lower, or vertical 

 part, is often distinguished 

 is mostlv continuous with the 



FIG. 272. ORBITAL LOBULE AND ISLAND 

 OF REIL. 



orb. Orbital sulcus. 



ol. Olfactory sulcus. 



ar. Anterior, er. Superior, and pr. Posterior 

 sulci of Reil, the last opened by the removal 

 of the temporal Jobe. 



10. Internal. AO. Anterior, and PO. Posterior 

 orbital convolutions. 



c. Central lobe or island of Reil. 



IF, AF, and AP. Lower parts of the inferior 

 frontal, ascending frontal, and ascending 

 parietal gyri, constituting opercula. 



APS. Anterior perforated space. 



and post- 

 central. 



Convolu- 

 tions : 

 ascending 

 parietal 



as the inferior postcentral sulcus, and 

 following one. 



The superior postcentral sulcus ( ptc) continues the direction of the 

 ascending part of the intraparietal sulcus, and ascends behind the 

 upper half of the furrow of Rolando. It generally opens into the 

 intraparietal sulcus at the spot where the latter is directed backwards. 



The ascending parietal convolution (AP) is placed opposite the 



