Method XX 121 



Xllth emerge along the ventro-lateral line, while the Vth, Vllth, 

 Vlllth, IXth, Xth, and Xlth enter and emerge respectively 

 along the lateral line. Consult a descriptive text for the origin, 

 function, and distribution of each of the nervi cerebrales. Make 

 a sketch of the basis encephali, illustrating the position and 

 peculiarities of the nerves. 



II. DIVISIONS OF THE ENCEPHALON. 



With a sharp knife sever the right pedunculus cerebri 

 immediately posterior to the corpora mamillaria. Then turn 

 the specimen dorsal surface upward, press open the fissura 

 longitudinalis cerebri to expose the corpus callosum, and care- 

 fully divide the corpus callosum along the mid-line. Proceed 

 slowly. Note, lying just under the corpus callosum, another 

 tract of white substance, the fornix. Under the fornix, note the 

 ventriculus tertius, a cavity between the thalami optici. The 

 thalami are composed of gray substance. Note that they are 

 united across the ventricle by the massa intermedia (middle 

 commissure). If the fornix be divided carefully, there will be 

 found just under it a non-nervous membrane spreading over the 

 cavity of the ventriculus tertius. This membrane is the tela 

 choroidea ventriculi tertii (velum interpositum). At the pos- 

 terior end of the ventriculus tertius (recessus pinealis) is the 

 corpus pineale. Let this longitudinal incision join the first, or 

 transverse incision through the pedunculus cerebri, so as to 

 leave the corpus pineale intact and resting in position upon the 

 corpora quadrigemina (see fig. 2). Continue the division so 

 that the knife passes between the corpora mamillaria, splits the 

 tuber cinerium in halves, and passes through the middle of the 

 chiasma opticum. Return the half of the prosencephalon thus 

 removed to the formalin solution for later use. 



Now identify the following divisions of the encephalon : 



(a) Rhombencephalon. 



1. Myelencephalon (medulla oblongata). 



2. Metencephalon. 



Pons (Varoli). 

 Cerebellum. 



3. Isthmus rhombencephali. 



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