EXPLANATION OF THE PLATES. 469 



The striata (s. s.) are seen in section just ventrad of the lateral expansion of the callo- 

 sum, while the lower part of the figure is occupied by the thalami (th.), united by the 

 medicommissura (mcs.). Between each thalamus and the corresponding striatura is a 

 groove, the Sulcus limitans (81. li.}. 



The Columnae fornicis (Clm.f.) are divided nearly at a right angle with their course, 

 and at a point just dorsad of the crista (Crs.f.), which is particularly well shown in this 

 preparation. The open space between the fornix and the thalami is the aula (a.), and at 

 the sides are the portae (p.] leading into the procodice. All the membranes and plexuses 

 have been removed. 



PLATE IV. 



Unlike those of Plate III, all of the figures upon this plate represent cut surfaces, 

 although some natural surfaces are shown also. 



1172. Fig. 14. A ventro-caudal view of the fornix, with the adjacent parts. 

 From Prep's 507, 433 and 396 (adult 6 ) ; x 2. 



The preparations were made while the brain was fresh, so as to permit more flattening 

 of the hemispheres, and consequent exposure of the fornix. 



After the removal of the rhinen-, meten-, epen- and mesencephalon, the thalami and 

 geniculata were excavated piecemeal, so as not to injure or displace the fornix. The cut 

 surface (s ) at each side of the fornix (/.) is the plane of division of the diencephalon from 

 the striatum. 



The cephalic end of the prosencephalon was then sliced down to the level of the prce- 

 commisxura (prcs.), which is seen to send a distinct fasciculus toward the L. olfactorius on 

 each side. Then the right hemisphere was sliced obliquely from near the meson dorso- 

 laterad so as to cut the medicornu (mcu.) and hypocampa (hmp.) at about the middle of 

 their length. On the left side, the L. temporalis was allowed to fall somewhat by its 

 own weight so as to expose the fornix more fully. 



The velum and all the plexuses were removed so as to display the peculiar markings of 

 the fornix and its mesal area, which is supposed to represent the lyra (ly.). 



The portae (p.) appear both shorter and narrower than they really are, on account of 

 the obliquity of their planes to the line of vision. The v-shaped line called ripa (rp.), 

 which connects the two portse, separates the delta (alt.) or entocoelian part of the fornix 

 from the remaining .surface, which is wholly outside of the coelian cavity. The delta 

 forms the roof of the aula, the cephalic continuation of the diacoelia between the two 

 portse, and the ripa is the line of reflection of the endyma upon the two auliplexuses ; the 

 removal of these plexuses causes the rupture of the endyma along the ripa. 



At each side, the ripa curves dorsad somewhat sharply so as to reach the dorsal end of 

 the porta ; at this point, and dorso-caudad for the entire length of the rima (r.), the 

 endyma is simply reflected from the contiguous surfaces of the fimbria (fmb.) and the cor- 

 responding border of the striatum. Hence the rima is virtually closed, and thus wholly 

 distinct from the porta. 



On the meson, between the portae, is seen the crista (Crs. /.), which is unusually 

 rounded in this preparation. The carina, which sometimes appears as a slight mesal ridge 

 extending dorso-caudad from the crista, does not appear in this preparation. The Reces- 

 sus aulae (R. a.) is the cleft between the two Columnae fornicis (Clm.f.) whose cut ends 

 are seen just caudad of the praecommissura. The shading on the caudal aspect of the 

 columnse indicates, but rather too distinctly, a slightly depressed area, of which the dorsal 

 part, close to the crista, sometimes presents the appearance of a transverse band, for which 

 the senior author has suggested the name Commissura fornicis (Cs. /.). 



