Dissection of Sheep* s Brain. 173 



iiig cornu, is the Choroid Plexus : in front it is conjoined 

 with, the Choroid Plexus of the other side, through a large 

 oval aperture (as it appears in this section), termed the Fora- 

 men of Monro : it rests upon the Corpus Fimbriatum or Tcenia 

 Hippocampi, which is a narrow white tape- like band attached 

 along the inner border of the curved elongated eminence that 

 extends along the entire length of the floor of the descending 

 cornu, and is called Hippocampus Major or Cornu Ammonis 

 (from its resemblance to a ram's horn). The Corpus Fimbria- 

 tum is a continuation of the lateral edge of the posterior 

 pillar of the Fornix. Just anterior to the edge of the Corpus 

 Fimbriatum, and underlying it, is a part of the eminence, 

 called the Optic Thalamus, into which the Optic tracts at the 

 base of the Brain are distinctly traceable. Running along 

 the part of the Optic Thalamus just mentioned is seen the 

 Choroid Arterij ; it arises either from the trunk of the inter- 

 nal carotid or from the middle cerebral artery, just at that 

 point where the inferior end of the fissure of Sylvius 

 meets the anterior end of the transverse fissure ; enters the 

 horn of the lateral ventricle, beneath the edge* of the 

 ' middle ' lobe of the Brain ; and is distributed to the Hippo- 

 campus Major, Corpus Fimbriatum, and Choroid Plexus. 

 The arteries of the Choroid Plexus, after ramifying through 

 its substance, send branches into the substance of the Brain ; 

 the veins of the Choroid Plexuses terminate in the Yenee 

 Galeni. 



On holding up the Brain to the light, and gently raising 

 the Corpus Callosum into its normal position, the thin semi- 

 transparent Septum Lucidum, which is attached above to the 

 under surface of the Corpus Callosum, and below to the 

 anterior part of the Fornix, is apparent. The Septum con- 



* Through the same part of the transverse fissure that the Choroid artery 

 enters the Brain, the Choroid Plexus joins with the Pia Mater. 



