THE BKAIN IN THE EDENTATA. 



309 



There is a marked contrast between the fomily type of dorsal commissure met witli in the 

 Brudijpodidie and the equally Avell-defined family type of the Dasupodidtc (fig. 23, p. 320). 

 In the latter we find that specialized form of psalterium which we have seen in the 

 Ilyrmecophagidce and Orycteropus, and which is found in the vast majority of Eutlieria 

 —a form of psalterium which we associate with a fully-developed corpus callosum. 

 The diminutive size of the corpus callosum in the Armadillos therefore sviggests a retro- 

 gressive development from some form witli a large corpus callosum. 



Eig. 18. 



hippocsmp. vestigia 



Corp. callos. 



Corp. quadrigem 



psalterium 

 bmbria 

 faBCia deotata 

 Jiippocamp. inversus 



tract, opt 



tobercul. olfact. 



; lob! pytiform. 



poD8 Varoi. 



rorji, interped- 



commiaa. moll. 

 Jytiform. vent, i 



fisB. hippocampi 



Brain of Cholapiis duhniiihis ; surface exposed by Ille.■^lal sagittal section. Enlarged .! diam. 

 The brain-stem has been cut away from the hemisphere. 



In the Bradijpodidiv we tind a marked contrast in the shape of the commissures. 

 Here we have a corpus callosum Avhich lias attained a much larger size than in the 

 Dasypodida', though we must still regard it as relatively small and primitive. The 

 psalterium presents a simple form in the Sloths, which a comparison with the marsupial 

 would point out as a primitive type. In other words, we might regard it as the result 

 of a progressive development from some simpler type rather than a retrogressive modifi- 

 cation of a more highly organized form, as may have been the case in the Armadillos. 



In all the Armadillos the ventral or anterior commissure is relatively very large, just 

 as we should expect from the large size of the pyriform lobe. 



In the brain of Manis the corpus callosum is very short, being barely 6 mm. long in 

 the specimen at my disposal, and almost of imiform thickness throughout. It does not 

 taper anteriorly, nor, on the contrary, is it thickened or bent anteriorly to form a genu. 

 In my specimen the corpus callosum was not nearly so thick and plump i]i proportion to 

 its length as that figured by Ma.^ Weber *. 



Max Weber has not figured the whole of the psalterium, but this structure in my 

 specimen appears to be clearly composed of two parts — a ventral and a dorsal, neither of 

 which is very plump. So that, on the whole, the dorsal commissure of Jlanis is mitcli 

 more like that of Eriiiaceus than any of the Edentates ; for, while the psalterium resembles 

 that found in the Dasypodldce, the corpus callosum is more like that of the BradypodidcB 

 in shape, size, and position. 



The anterior commissure is moderately large. 



* Max Weber, op. cit., ' Zool. Ergebnisse,' ii. tab. i.v. fig. (j9 co. 

 SECOND SERIES. — ZOOI.OGY, VOL. VII. 



43 



