882 



THE NERVOUS SYSTEM 



Its upper surface shows a middle, an anterior, and a posterior prominence or tuber- 

 cle. The anterior tubercle (nucleus) forms the posterior boundary of the inter- 

 ventricular foramen; the posterior tubercle is the cushion-like pulvinar which 

 projects backward over the lateral geniculate body and the brachium of the 

 superior quadrigeminate body. 



A horizontal section through the supero-medial edge, splitting the stria medul- 

 laris of the thalamus and thus passing above the massa intermedia, shows the grey 

 mass of the thalamus divided into segments or nuclei by a more or less distinct 

 internal medullary lamina. This extends the whole length of the thalamus, 

 dividing its middle and posterior portion into the medial and the lateral nucleus. 



Fig. 694. — Horizontal Dissection showing the Grey and White Substance of the 

 Telencephalon Below the Corpus Callosum and the Relatwe Position of the 

 Thalamencephalon. (After Landois and Stirling.) 



Gyrus cinguli 



Genu of corpus callosum 



Anterior cornu 



Caudate nucleus 



Internal capsule 

 (Frontal portion) 



External capsule 

 , ^. , ( Putamen 

 Lenticular Globus 



nucleus ( pallidus 

 Claustrum 

 Internal capsule (occi- 

 pital portion) 



Thalamus 



Medial geniculate 

 body 

 Tail of caudate 

 nucleus 

 Hippocampus major 



Hippocampus minor 



^■-r-Septum pellucidum 



•^^ Corpus striatum 

 Column of fornix 



Stria terminalis of 

 thalamus 



Funiculus cuneatus 

 Funiculus gracilis 



Anteriorly the lamina bifurcates into a medial limb, extending to the medial sur- 

 face of the thalamus, and a lateral limb, extending forward to join the genu of the 

 internal capsule (figs. 695, 700). This bifurcation results in a cup-like sheet of 

 white substance which encloses the anterior nucleus. On the lateral surface of 

 the section, next to the internal capsule, there may usually be distinguished an 

 external medullary lamina, separated from the white substance of the capsule 

 by a reticular layer of mixed white and grey substance. 



The anterior nucleus, lying partially encapsulated in the bifurcation of the 

 internal medullary lamina, is somewhat wedge-shaped and points backward be- 

 tween the anterior portions of the lateral and medial nuclei. 



It is composed chiefly of large cells, and constitutes the anterior tubercle of the superior 

 aspect. Its principal connection from below is with the nuclei of the mam miliary body of the 

 same and opposite sides, and with uninterrupted fibres derived from the columns of the fornix. 



iA 



