524 



NERYOUS SYSTEM. 



The corpus fimbriatum, called also the tsenia hippocampi, is a narrow, white, 

 tape-like band, situated immediately behind the choroid plexus. It is the lateral 

 edge of the posterior pillar of the fornix, and is attached along the inner border of 

 the hippocampus major as it descends into the middle horn of the lateral ventricle. 

 It may be traced as far as the pes hippocampi. 



The thalami optici and fornix will be described when more completely exposed, 

 in a later stage of the dissection of the brain. 



The middle cornu should now be exposed, throughout its entire extent, by introducing the 

 little finger gently into it, and cutting through the hemisphere, between it and the surface, in the 

 direction of the cavity. 



The middle or descending cornu, the largest of the three, traverses the middle 

 lobe of the brain, forming in its course a remarkable curve round the back of the' 



Fig. 268. The Fornix, Velum Interpositum, and Middle or Descending Cornu of 

 the Lateral Ventricle. 



optic thalamus. It passes, at first, backwards, outwards, and downwards, and 

 then curves around the crus cerebri, forwards and inwards, nearly to the point of 

 the middle lobe, close to the fissure of Sylvius. Its upper boundary is formed 

 by the medullary substance of the middle lobe, and the under surface of the 

 thalamus opticus. Its lower boundary presents for examination the following 

 parts : The hippocampus major, pes hippocampi, pes accessorius, corpus fimbria- 

 tum, choroid plexus, fascia dentata, transverse fissure. 



The hippocampus major or cornu ammonis, so called from its resemblance to 

 a ram's horn, is a white eminence, of a curved elongate form, extending along the 



