THE CENTRAL SULCUS 



859 



the somaesthetic area of the mesial surface of the hemisphere. This lobule is 

 usually marked off anteriorly by a vertical twig from the sulcus cinguli. 



The sulcus cinguli (calloso-marginal fissure) is the longest and one of the most 

 prominent sulci on the mesial surface of the hemisphere. It divides the anterior 

 portion of the mesial surface into a marginal part above and a callosal part below 

 — in other words, it separates the superior frontal gyrus from the gyrus cinguli. 

 Its subfrontal portion begins below the rostrum of the corpus callosum and curves 

 forward and upward around the genu, and then turns backward above the body 

 of the corpus callosum. Before it reaches the level of the splenium, it turns up- 

 ward and cuts and terminates in the supero-mesial border of the hemisphere, as 

 the next sulcus behind the upper termination of the central sulcus. This upward 



Fig. 676. — Basal Surface of the Cerebral Hemispheres. (After Toldt, "Atlas of Human 

 Anatomy," Rebman, London and New York.) 



Longitudinal fissure 

 J 



Frontal pole 

 Olfactory sulcus 



Orbital sulci 



Olfactory bulb 



Olfactory tract 



Temporal pole -^ 

 Olfactory trigone,. 



Optic chiasma — 

 Chorioid fissure 



Collateral fissure -■ 



Medial, intermediate, and 

 lateral olfactory striae 



Anterior perforated 

 X substance 



Limen of insula 



Lateral fissure 

 - (Sylvii) 



Inferior temporal 

 sulcus 



Isthmus of gyrus fornicatus 



Gyrus fornicatus 



Nucleus of 



amygdala 



Peduncle of 

 ■ cerebrum 

 (basis pe- 

 dunculi) 



|:^^ Posterior 



perforated 

 913 substance 



Substantia nigra 



Tegmentum of 

 mesencephalon 



Occipital pole 



Aquseductus cerebri 

 (Sylvii) 



Lamina quadrigemina 

 Splenium of corpus callosum 



Longitudinal fissure 



turn is the marginal portion of the sulcus cinguli. It is sometimes an abrupt 

 curve and sometimes curves gradually, but its marginal relation to the upper end 

 of the central sulcus is so constant that it serves as a means by which either of the 

 sulci may be identified. The marginal portion separates the paracentral lobule 

 from the precuneus (quadrate lobule), and is wholly within the parietal lobe. 

 One of the most constant twigs of the sulcus cinguli is that which marks off the 

 paracentral lobule from the superior frontal gjTus. x\nother sometimes divides 

 the paracentral lobule into its frontal and parietal portions. 



The sulcus cinguli is developed from two and sometimes three (anterior, middle, and pos- 

 terior) separate furrows, which later extend and fuse into continuity. This method of its 

 development may explain the irregularities frequently met with and the fact that sometimes 

 in the adult the sulcus occurs in separate pieces. 



The central sulcus (fissure of Rolando) (figs. 674, 678) is one of the principal land- 

 marks of the convex surface of the hemisphere. It separates the frontal from the 

 parietal lobe, and likewise divides the somsesthetic area of the pallium. Its 



