:<><> 



Comparative Morphology of Chordates 



fissure of Sylvius on the external side of the hemisphere, separating 

 the frontal lobe from the temporal lobe, which is below and behind 

 the fissure (Fig. 524). In the human brain parietal and occipital 

 lobes also are recognized. These lobes are merely topographic, but 

 are not functionally distinct. 



The question arises as to why a given volume of cortical substance 

 should be disposed in this elaborately folded manner rather than in the 

 form of a thicker layer lying smoothly over a smooth surface of "white 

 substance." It is as if the cortex had been unable to increase in thick- 

 ness as it increased in volume and accordingly was compelled to develop 

 wrinkles. Certain advantages of the convoluted arrangement can be 

 recognized. The innermost investing membrane of the brain, the pia 

 mater, thin but richly vascular, is folded deeply into all the fissures 



ANGULAR GYRUS 



FRONTAL POLE 

 ORBITAL GYR 



FISSURE OF S 

 SUPERIOR TEMPORAL GYRUS 

 MIDDLE TEMPORAL GYRUS 



TEMPORAL 



TEMPORAL POLE' 



INFERIOR TEMPORAL GYRUS 



c 



OCCIPITAL LOBE 

 OCCIPITAL POLE 



Fig. 524. Lateral views of brains of (A) rabbit, (B) dog, and (C) man. {B.ol) 

 Olfactory lobe; (////) cerebellum; (Hyp) hypophysis; (Med) spinal cord; (NH) 

 medulla oblongata; (Po) pons Varolii; (VH) cerebral hemispheres; (Wu) median 

 vermis of cerebellum; (II-XII) cranial nerves. (A and B, courtesy, Wiedersheim : 

 "Grundriss der vergleichenden Anatomie der Wirbeltiere," Jena, Gustav Fischer. 

 C, after Sobotta. Courtesy, Neal and Band: "Comparative Anatomy," Phila- 

 delphia, The Blakiston Company.) 



