CHAPTER VIII 



THE GENERAL TOPOGRAPHY OF THE BRAIN. THE EXTERNAL 

 FORM OF THE MEDULLA OBLONGATA, PONS, AND MESEN- 

 CEPHALON 



The General Topography of the Brain. The brain rests upon the floor of 

 the cranial cavity, which presents three well-marked fossae. In the posterior 

 cranial fossa are lodged the medulla oblongata, pons, and cerebellum, which 

 together constitute the rhombencephalon (Fig. 81). This fossa is roofed over 

 by a partition of dura mater, called the tentorium cerebelli, that separates the 

 cerebellum from the cerebral hemispheres. Through the notch in the ventral 



Calvaria 



Prosen-( Telencephalon 

 cephalon\Diencephalon 



Frontal lobe of cerebral 



hemisphere in anterior 



cranial fossa 

 Temporal lobe of cerebral 



hemisphere in middle 



cranialfossa 



Parietal lobe of cerebral 

 hemisphere 



Mesencephalon 



Occipital lobe of cerebral 



hemisphere 

 Tentorium cerebelli 

 Posterior cranialfossa 



Cerebellum 



Pons 



Medulla oblongata 



Spinal cord 



Fig. 81. Median sagittal section of the head showing the relation of the brain to the cra- 

 nium. The sphenoid bone is shown in transparency, and through it the temporal lobe may be 

 seen. 



border of the tentorium projects the mesencephalon, connecting the rhomben- 

 cephalon below with the prosencephalon above that partition. The cerebral 

 hemispheres form the largest part of the prosencephalon, occupy the anterior 

 and middle cranial fossae, and extend to the occiput on the upper surface of the 

 tentorium. 



The dorsal aspect of the human brain presents an ovoid figure, the large 

 cerebral hemispheres, covering the other parts from view. In the sheep's brain the 



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