

THE FORE-BRAIN OR PROSENCEPHALON 



and postero-laterally by the diverging cerebral peduncles. The structures con- 

 tained in it have already been described; from behind forward, they are the pos- 

 terior perforated substance, corpora mamillaria, tuber cinereum, infundibulum, 

 and hypophysis. 



Frontal lobe 



Temporal 

 lobe 



Occipital lobe 



FIG. 724. Base of brain. 



The Telencephalon. The telencephalon includes: (1) the cerebral hemispheres 

 with their cavities, the lateral ventricles; and (2) the pars optica hypothalami and 

 the anterior portion of the third ventricle (already described under the dienceph- 

 alon). As previously stated (see page 744), each cerebral hemisphere may be 

 divided into three fundamental parts, viz., the rhinencephalon, the corpus 

 striatum, and the neopallium. The rhinencephalon, associated with the sense 

 of smell, is the oldest part of the telencephalon, and forms almost the whole of 

 the hemisphere in some of the lower animals, e. g., fishes, amphibians, and 

 reptiles. In man it is rudimentary, whereas the neopallium undergoes great 

 development and forms the chief part of the hemisphere. 



The Cerebral Hemispheres. The cerebral hemispheres constitute the largest 

 part of the brain, and, when viewed together from above, assume the form of 

 an ovoid mass broader behind than in front, the greatest transverse diameter 

 corresponding with a line connecting the tw r o parietal eminences. The hemispheres 

 are separated medially by a deep cleft, named the longitudinal cerebral fissure, 

 and each possesses a central cavity, the lateral ventricle. 

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