36 TOPOGRAPHIC AND APPLIED ANATOMY. 



PLATE 3. 

 The base of the brain with the twelve cranial nerves and the cerebral arteries. 



The incisura tentorii transmits the so-called isthmus cerebri, which is formed ventrally by 

 the crura and dorsally by the corpora quadrigemina. The occipital lobes of the cerebrum rest 

 upon the tentorium; the lower surface of the tentorium covers the upper surface of the cere- 

 bellum, the hemispheres of which fill the deepest portions of the posterior cranial fossa (fossae 

 occipitales). The pons lies upon the upper two-thirds of the clivus, its anterior border almost 



Sagittal sutun 

 Cerebral veins-- 



-Scalp 



Superior longi- 

 tudinal sinus 



Occipital lobe 



Straight sinus 



Lambdoidal suture 

 Transverse sinus 



Fall cerebelli 

 Occipital bone 



FIG. 12. A frontal section through the posterior portion of the head (frozen section). Anterior view. The 

 section strikes the falx cerebri, the falx cerebelli, and the tentorium cerebelli in such a way that the cranial cavity seems 

 to contain four apparently separate compartments, in which may be seen the two cerebral and the two cerebellar 

 hemispheres. 



reaching to the dorsum of the sella turcica. The lower third of the clivus, as far down as the 

 foramen magnum, lodges the anterior portion of the medulla oblongata which extends to the 

 upper margin of the posterior arch of the atlas. A median sagittal section (see Plate 4) shows 

 that the pons and medulla assume an almost vertical position. It should also be observed that the 

 cerebrum is much more exposed to external injuries than is the better protected cerebellum. 



As it is occasionally necessary to open the cranial cavity and expose definite regions of the 



