LOBES OF THE CEREBRAL HEMISPHERE. 747 



somewhat as it runs backwards ; and at its termination it is 

 bent upwards for a short distance and projects into the parietal 

 lobe. 



When the brain is in the skull, the place of division of the Position in 

 fissure of Sylvius is opposite the articulation of the great wing fjJue^JJf* 

 of the sphenoid with the parietal bone ; or opposite a point one head, 

 and a quarter inches behind the external angular process of the 

 frontal bone and quarter of an inch above the level of that process 

 nn the undissected head. 



The sulcus of Rolando (central sulcus ; fig. 270, r] crosses the Sulcus of 

 outer surface of the hemisphere near the middle. Beginning above Rolando 



to the margin of the great longitudinal fissure, the furrow 

 runs downwards and somewhat forwards, with a serpentine course, 

 to end about one inch behind the place of division of the Sylvian 

 fissure, and very near to its posterior limb. This sulcus separates 

 the frontal from the parietal lobe. 



The upper end of the furrow of Rolando is placed from an is behind 

 inch-and-a-half to two inches behind the coronal suture, and the suture, 

 lower end about one inch. In the undissected head its upper end 

 is half an inch behind a point midway between the glabella and 

 the external occipital protuberance, measured along the convexity of 

 the skull, and the general direction of the sulcus is downwards and 

 forwards towards the mid-point of the zygoma. 



The parieto-occipital fissure (fig. 270 and fig. 273, p. 753, po) is Parieto- 

 a deep hollow at the hinder part of the inner surface of the hemi- assure; 

 sphere. Its upper end appears on the superior surface of the 

 cerebrum about midway between the sulcus of Rolando and the 

 posterior extremity of the hemisphere, and extends outwards for 

 nearly an inch from the margin of the longitudinal fissure. It 

 indicates the anterior limit of the occipital lobe. The part on the 

 mesial surface of the hemisphere is often called the internal, and 

 that on the outer surface the exit-null [xirieto-occipital fissure. 



The fissure is placed opposite the summit of the lambdoid suture, situation. 



LOBES. The outer surface of the hemisphere is divided into five Lobes of 

 lobes (excluding the olfactory) which have the following names and 

 limits : 



The frontal lobe forms the anterior half of the hemisphere. It is Frontal lobe 

 limited below by the posterior branch of the fissure of Sylvius lb largest 

 (fig. 270, s'"), and behind by the sulcus of Rolando (r). Its under 

 part, which rests on the roof of the orbit, is named the orbital orbital 

 lobule. lobule ' 



The parietal lobe is little more than half the size of the frontal. Parietal 

 Its anterior limit is the sulcus of Rolando (r), and its posterior a 1 ' 

 line drawn transversely over the hemisphere from the parieto- 

 occipital fissure. Below, it is bounded in its fore part by the boundaries 

 posterior branch of the fissure of Sylvius (*'"), and in its hinder j )a e rt m grea 

 part by a line extending backwards from the spot where this artificial. 

 fissure turns upwards to the line drawn transversely outwards from 

 the parieto-occipital fissure. This limitation of the lobe is quite 

 arbitrary and can be used only for descriptive purposes, since its 



