THE CEREBRUM 



443 



and so are prolonged, in the inferior horn, into the fimbria 

 and the alveus. They constitute a transverse commissure 

 from one hippocampus to the other. 



Dissection. The body of the fornix should now be divided 

 transversely, across its middle. Its posterior and anterior 

 portions may then be raised from the tela chorioidea of the third 

 ventricle, and thrown apart from each other. Had it been 

 possible to raise the corpus callosum and fornix together, the 



Cavum septi pellucidi Genu of corpus callosum 



Fornix (divided) . 



Stria 

 terminalis "-/J 



Septum pellucidum 

 .- Caudate nucleus 



Column 

 of fornix 



Tela chorioidea 

 of third ventricle 



Internal cerebral 

 Cru 



jralvein' / /.. 



V / ^ 



rus of fornix 



Chorioid plexus 



Body of fornix 

 reversed 



FIG. 174. Dissection to show the Tela Chorioidea of the Third 

 Ventricle and the parts in its vicinity. The fornix has been 

 divided and thrown backwards. 



diverging crura of the fornix would have been seen to limit a 

 triangular space on the under surface of the corpus callosum, 

 anterior to the posterior margin of the splenium. That interval 

 is termed the lyra ; it is traversed by a series of oblique markings 

 which indicate the presence of the transverse fibres passing 

 across from one crus of the fornix to the other. 



Tela Chorioidea Ventriculi Tertii (O.T. Velum Inter- 

 positum). The tela chorioidea of the third ventricle consists 

 of two layers of pia mater which form a fold of triangular 

 outline. It intervenes between the body of the fornix, above, 

 and the roof of the third ventricle and the two thalami, 



