CEEEBRAL COMMISSURES IX THE VEKTEBKATA. 



491 



characteristic choroid plexus. The distal attachment of this fold is to the ventral lip 

 of the fascia dentata. 



If, however, a section (fig. 26) he made Ijehind the situation marked x-y in the figure 

 representing the rooL' (Hg. 23), the typical thalamic roof is found to have no connection 

 with the lateral plexvis. The dorsal attachment of the latter is still to the margin of the 

 lascia dentata, while its ventral extremity is inserted into the " tcenia chorioidea " (His), 



ter 



Section piissing- buliiiid the foramen ol Monro. 



i. e. the stria terminalis. In the whole of the caudal extent of the ventricle the choroid 



plexus presents similar attachments to the margin of the fascia dentata and the stria 



terminalis (fig. 2G). 



Fig. i;7. Fig. 2?^. 



Fig. 27 shows the ])rimitive relation oi' 

 the optic thalamus to the posterior 

 lip of the cerebral hcmisplicre. 

 The backwai-d extension of the 

 hemisphere will stretch the attach- 

 ment to the optic thalamus at *, 

 and reduce it to the condition of a 

 thin epithelial lamina as in the 

 next figure. 



jPcy. 



Schemata to explain how the posterior choroidal fold may arise. 



Now, although in the whole of its extent the epithelial layer of the choroid plexus 

 presents uniform features, it is difficult to admit a common origin for the whole 



