456 ANATOMICAL TECHNOLOGY. 



and the existence of something like the terminal expansion which, 

 in the human brain, is called the "pe* hypocampa.'''' 



§ 1148. Demonstration that the Hypocampa is only a Modified 

 Portion of the Procoelian Parietes. — Carefully pass the tracer be- 

 tween the opticus and the caudal border of the hemisphere, and 

 rotate it so that the point may penetrate the hypocampa and appear 

 in the medicomu. Withdraw the instrument without disturbing 

 any connections ; see Pig. 121 and PI. IV, Fig. 18, 19. 



§ 1149. Opening the PrcBcornu and Exposure of the Striatum. — 

 From the roof of the procoelia, cephalad of the orifice first exposed, 

 remove a thin wedge-shaped slice, and thus more completely expose 

 ihe fornix, which is seen to be continued along the cephalic border 

 of the hypocampa as a flat band, the fimbria. 



Cephalad of the fornix is a marked elevation, the striatum ; that 

 part of the procoelia into which it projects is the praecomu. Be- 

 tween the striatum and the fornix and fimbria is a depression, the 

 Stilcus Umitans, into which projects a plexus, the proplexus. The 

 sulcus and the plexus may be traced along the cephalic border of 

 the fimbria to near the tip of the medicornu ; their relations will be 

 seen better at a later stage of the dissection. 



Note that the cella media does not quite reach the meson, on 

 account of the continuity of the fornix and the hypocampa with the 

 callosum. As will be seen later, the only place where the procoelia 

 does reach the meson is at the bottom or mesal end of the Sulcus 

 limitans, where the porta communicates with the aula and thus 

 with the mesal series of coelise. 



Exposure of the Mesal Aspect of the Striatum. — Along a line 

 passing dorso-ventrad about 2 mm. cephalad of the chiasma, make 

 an incision 1 mm. deep at the venter, its dorsal end reaching the 

 mesal border of the striatum, as already exposed. 



From the mesal aspect of the olfactory lobe and cephalic part 

 of the hemisphere remove a slice about 1 mm. thick, and then, with 

 the small scalpel, cut successively thin wedge-shaped slices so as to 

 expose the mesal aspect of the striatum and the cavity, the pr(Z- 

 cornu, into which it projects. Note the somewhat sharply defined 

 ridge which separates the mesal from the dorsal surface of the stria- 

 tum, and the greater extent of the former. 



§ 1150, Opening the Rhinocoelia. — The ventro-cephalic angle of 

 the prsecornu presents a slight funnel-shaped prolongation, which 

 may be traced cephalad into the Crus olfactorium, and to within 



