DEMONSTRATION OF THE PBOCCELIA. 455 



of the caUoswn, and make a slight incision. Then dip the scalpel 

 in alcohol, and cut horizontally along that line so as to remove the 

 dorsal part of the hemisphere. 



On the surfaces so exposed note the ental alba (centrum ovale) 

 and the ectal cinerea (cortex) ; also the undulations of the line of 

 tlieir junction, according to the depth of the fissures between the 

 gyri. Slice the removed dorsal piece in various directions so as to 

 shovr the continuity of the cinerea. 



If the surface of the alba of the ventral part is uniform in color 

 and continuous, remove successive slices, not more than .5 mm. 

 thick, until, about 5 mm. from the meson, there appears a group of 

 dark points ; the removal of another very thin slice will then expose 

 the summit of an arched cavity, the cella media of the proccelia, 

 and a slightly undulating convex surface, the cephalic part of 

 which is the fornix and the caudal the hypocampa (" hippocampus 

 major"). 



Opening tlie Medicornu and Exposure of the Hypocampa. — 

 Push the syringotome very cautiously latero-caudad between the 

 hypocampa and the cut edge which overhangs it, and then, with 

 the scalpel, remove a wedge-shaped slice so as to expose more of 

 the hypocampa. Repeat the operation, bearing in mind that the 

 direction of the hypocampa and of the cavity — the medicornu — into 

 which it projects, is successively caudad, laterad, ventrad, cephalad 

 and mesad ; see Fig. 119. 



The anthropotoniical terms indicative of these directions are backward, outward, down- 

 ward, forvjard and inward, the initial letters of which form the mnemonic word bodfi. 



During this exposure of the hypocampa, there is danger that some 

 part of its surface will be sliced off, and the syringotome should be 

 used as an explorer before each incision. When near the tip of the 

 LI. hypocampcB, be especially careful not to cut too deeply ; the tip 

 of the cornu is here separated from the ectal surface by a very thin 

 lamina. 



When the entire length of the hypocampa is exposed, pass the 

 convexity of the tracer along its caudal border, and then slice off the 

 overhanging portions of the caudal wall of the medicornu. Note 

 that the width of the medicornu varies somewhat, but that there is 

 no sign of the caudal prolongation which, in man, the monkeys, 

 seals and some cetacea, forms a postcornu. ]S"ote also two slight 

 oblique ridges which cross the hypocaimpa in opposite directions, 



