Dissection of Sheep's Brain. 179 



upper surface of the Pons, roofed in by tlie Yalve of Yieus- 

 sens, and then passing into the fourth Yentricle beneath the 

 Cerebellum, to terminate at the Calamus Scriptorius and Yalve 

 of Arantius, the anterior extremity of the closed central canal 

 of the spinal cord. In the Cerebellum there will be noted the 

 absence of any enclosed cavity or ventricle, such as was found 

 in the Cerebrum ; but, instead, the presence of a mass of 

 white matter in the centre which sends out spreading and 

 gradually thinning layers into the interior of all the laminae of 

 the grey substance which forms a continuous covering on the 

 surface ; and, as the consequence of this arrangement of the 

 grey and white substances, the presence of a beautiful foliation 

 or arborescence, named * Arbor vitae ;' the section, above made, 

 crossing the laminas and dividing the grey and white sub- 

 stances together. 



