THE BEAIN IN THE EDENTATA. 319 



hippocampal fissure even appears to extend into contiuuity with the callosal fissnn;. 

 Looking at the mesial surface of the hemisphere, the upper part of the fascia dentata 

 appears to accompany the fimbria right up to the splenium and then to pass without any 

 marked bending into the vestigial hippocampus which covers the dorsal surface of the 

 corpus callosum. 



A large supracaliosal hippocampal vestige is found in both Sloths, and in my specimen 

 of Bradijpus we have an interesting demonstration of the precallosal course of the hippo- 

 campal vestige. Thus we find extending obliquely downward and forward from the 

 front of the corpus callosum two shallow furrows which slightly diverge as they approach 

 the olfactory peduncle (fig. 17). The upper of these furrows corresponds to the limiting 

 fissure of the pallium in the 3Iijr7necophagid(B . The area included between these two 

 furrows is the precallosal part of the hippocampal vestige. It appears broader than the 

 supracallosal part of the vestigial arc because the latter is flattened horizontally upon the 

 corpus callosum, while the precommissural vestige is vertical, being a constituent part of 

 the mesial wall of the hemispheres. 



In representing the hippocampus from any one point of view it is impossible to convey 

 an accurate idea of its exact disposition, because it bends about in various planes during 

 its course so that in a perspective drawing it appears distorted. As it is a matter of great 

 importance to clearly understand the behaviour of this importaut and peculiar part of the 

 brain, I have drawn three schemes (fig. 23) : one of Tamandua, representing the Ant- 

 eaters; one o? Choloepns, representing the Sloths, which Ave have already discussed; and 

 one of Dasi/p'us villosus, representing the Armadillos, which we shall consider almost 

 immediately. These schemes represent the actual relations of the hippocampal formation 

 to the commissures in the three American families of Edentates. 



After the preceding descriptions these schemes are almost self-explanatory. In the 

 Ant-eater (A) we see the three bands of fimbria (Ji-), inverted hippocampus (i.h.), and 

 fascia dentata (f.d.) ascending in front of the hippocampal fissure (h.f.), just as they do 

 in the Rabbit or any of the common Eutheria. As they ascend, the intermediate band 

 (inverted hippocampus) disappears and the fascia dentata comes into contact with the 

 fimbria. Tlie main portion of the latter continues its forward course to the p)salte)'lmn_ 

 ventrale (;ps.v.), but a few of its uppermost fibres become widely scattered in tlie 

 triangular interval bet^veen the subsplenial flexure of the fascia dentata (f.d.'} and the 

 fibres going to the ventral part of the psalterium. Erom these scattered fibres the thin 

 Taemhranous psalterium doi^sale (ps.d.) is formed. The fascia dentata (/.''/.) suddenly 

 diverges from the fimbria and bends backward beneath the splenium (spl.) of the corpus 

 callosum. As it does so it rapidly tapers and fades away. As this is taking place a part 

 of the true hippocampus (u.h.) (using that term in the strict and exclusive sense) crops 

 out of the upper part of the hippocampal fissure (hf). This little fragment of naked 

 hippocampus {n.h.) becomes directly continuous with its atrophied serial homologue, the 

 vestigial hippocampus {v.Ji.), which surrounds the corpus callosum (c.c.) and extends 

 forward not only as far as the genu {(/.), but beyond this point toward the situation of 

 the olfactory peduncle. 



U* 



