762 DISSECTION OF THE BRAIN. 



Ttenia Along the inner margin of the hippocampus is the toenia hippo- 



hippocampi. cam ^ Qr fi m i r i a (fig. 76, c), which is the prolonged posterior 

 pillar of the fornix ; this ends below by joining the recurved part 

 of the uncinate convolution. 



Dissection. Dissection. To examine more fully the hippocampus, the 

 hinder portions of the corpus callosum and fornix should be divided 

 in the middle line, and the posterior part of the right hemisphere 

 should be drawn away from the rest of the brain. When the pia 

 mater has been removed from the inner side of the hippocampus, 

 and this projection has been cut across, its structure will be seen. 

 Structure The hippocampus is covered on the ventricular surface by a 



campus!" thh 1 medullary layer, with which the taenia blends. On its opposite 

 surface is the hollow of the hippocampal, or dentate, fissure of the 

 exterior of the brain, which is lined by grey substance. Beneath 

 the taenia hippocampi the grey matter projects in the form of a 

 notched ridge, the fascia dentata, or dentate convolution, which is 

 external to the cavity of the ventricle (p. 755). 



Collateral The EMiNENTiA coLLATERALis (fig. 275, fc), is the triangular, 

 rice ' slightly convex surface occupying the floor of the posterior and 

 descending cornua of the lateral ventricle to the outer side of the 

 formed by hippocampi. It lies over the collateral fissure of the under surface 

 fissure f the hemisphere, and its extent varies greatly in different subjects. 

 Amygdaloid The AMYGDALOID TUBERCLE is a variable eminence due to a col- 

 lection of S re y matter, amygdaloid nucleus (fig. 279, p. 768), on 

 the outer side of the uncus, with the cortical layer of which it is 

 continuous. 



Great trans- TRANSVERSE FISSURE OF THE CEREBRUM. By drawing the 



5SUre separated part of the right hemisphere away from the cms cerebri 

 and the optic thalamus, and replacing it, the dissector will com- 

 prehend the position and boundaries, on one side, of the great cleft 

 of the brain. 



is beneath This fissure lies beneath the fornix and splenium of the corpus 



reach* s a tme callosum, and above the optic thalami and corpora quadrigemina 



of brain. (fig. 274, p. 757) ; and in the dissected brain it opens into the 



lateral ventricle along the edge of the fornix on each side, from the 



foramen of Monro to the extremity of the descending cornu. The 



slit opening into the lateral ventricle (choroidal fissure) is bounded 



by the edge of the fornix with the taenia hippocampi above 



and by the optic thalamus and cms cerebri below. A fold of 



Pia mater pia mater (velum interpositum) projects into the transverse fissure 



beneath the fornix (fig. 276, </), and forms lateral fringes the 



choroid plexuses, which appear in the ventricles along the margins 



of the slit. In the natural state the fissure is separated from the 



cavity of the ventricle by the epithelium of the ependyma being 



continued over the choroid plexus, and therefore does not exist as a 



complete fissure except in the dissected specimen. 



Parts in the The student is now to return to the examination of the parts in 

 the brahi. the centre of the brain, viz., the fold of pia mater and its vessels, 

 with the third ventricle. Afterwards the corpus striatum and optic 

 thalamus will be studied. 



