1 1 8 Neurological Technique 



the Aa. cerebri anteriores of the two cerebral hemispheres are 

 connected by the short A. communicans anterior. 



Thus it will be seen that the communicating branches of the 

 larger arteries form, at the base of the brain, a circle about the 

 chiasma opticum and the corpora mamillaria. In the English 

 texts this is known as the "circle of Willis." It is made by 

 the Aa. cerebri posteriores, Aa. communicantes posteriores, Aa. 

 carotides internae, Aa. cerebri anteriores, and the A. communi- 

 cans anterior. 



(c) External features of the brain proper. — i . Fades convexa 

 (dorsal and lateral aspects). — Carefully remove whatever may 

 remain of the dura mater and arachnoidea, and lay the specimen 

 dorsal surface upward. Identify polus frontalis, polus occipitalis, 

 and fissura longitudinalis cerebri. Gently pull apart the cere- 

 bral hemispheres and note the corpus callosum. What is its 

 appearance compared with the rest of the encephalon ? Why ? 



Identify fissura cerebri lateralis (fissure of Sylvius), sulcus 

 centralis (fissure of Rolando), and gyri centralis posterior and 

 centralis anterior. Why is the fissura cerebri lateralis called 

 fissure instead of sulcus ? 



Lift apart the polus occipitalis from the cerebellum and note 

 the mesencephalon (corpora quadrigemina). Resting upon the 

 coUiculi superiores (anterior corpora quadrigemina) may be seen 

 the corpus pineale. 



Note the cerebellar hemispheres and vermis superior. Lift 

 the posterior margin of the cerebellum from the medulla 

 oblongata below, and note the vermis inferior and lobulus cen- 

 tralis. With the aid of an atlas or illustrated text, identify 

 more fully the various external features of the cerebellum. 

 What can be said of the size, depth, and arrangement of the 

 gyri and sulci of the cerebellum as compared with those of the 

 cerebrum ? Are there any variations to be noted in the bilateral 

 symmetry of the encephalon ? 



2. Basis encephali. — Now lay the brain ventral surface 

 upward and note the following: 



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