THE BK.AIN IN THE EDENTATA. 303 



2G mm. in lengtli aud 2'5 mm. iii thickness. The corjjus callosum in tlie specimen 

 which Forbes figures is about the same length, but not quite so thick. The cerebral 

 liemisjihere in Ilijrmecophaga is usually about 54 mm. long, so that the corjnis callosum 

 is almost half tlie lengtli of the hemisphere. 



In a specimen of Tamaudua, whose hemisjjhere is 34 mm. long, the corpus callosum 

 increases 14 mm. in length, and its narrowest part 1 mm. in thickness. 



Pouchet * rejjresents the mesial surface of tlie cerebral hemisphere of a Cyclutaras, the 

 corpus callosum of which is very narrow and 6-5 mm. long, the hemisphere itself being 

 17 mm. long. 



Thus we see that in the brains of the ]\Iyrmeco2)hagidse the corpus callosum is rela- 

 tively shorter in proportion as the animal is smaller, the corpus callosum measuring 

 respectively 48 per cent., 41 per cent., and 38 per cent, of the length of the hemisphere 

 in the three genera. 



In all the Armadillos the corpus callosum is very small. Pouchet describes the 

 corpns callosum in a young Dasypus, whose cerebral hemisj)here is about 23 mm. long, 

 as being mm. long and 1 mm. thick. Turner represents f in Dasyijus sescinct us the 

 cerebral hemisphere 30 mm. long, possessing a corpus callosum 6 mm. long aud 1 mm. 

 thick. lu the brain of Xenitrus, the cerebral hemisphere of which is 25 mm. long, we 

 tind a corpus callosum measuring o mm. in length and barely 1 mm. in thickness (in a 

 specimen preserved in alcohol). In ToUjpeutes the proportion is about the same. In a 

 cerebral hemisphere of Chlamydophorus, 11-5 mm. in length, we find a diminutive corpus 

 callosum of 2-25 mm. length and about '25 mm. thickness. 



In all the xirmadillos, in spite of the small dimensions of the cerebral hemisphere, the 

 proportion between the lengths of the corpus callosum and the hemisphere is much 

 smaller than it is in the Sloths, and, a fortiori, than in the Ant-eaters. 



In his figures of the brains of a Ilauis, Max Weber represents J a corpus callosum 

 G mm. long and 1'5 mm. thick in a hemisphere whose maximum length is 24 mm. 

 Pouchet represents ^ a corpus callosum 4'5 mm. ioug aud 75 mm. thick in the brain 

 of a young Manis, the hemisphere of which is 20 mm. long. In a cerebral hemisphere 

 of the same length as Weber's specimen I have found a corpus callosum 6 mm. long, 

 but barely 1 mm. thick. The disparity between these measurements of the thickness is 

 probably explained by the fact that Max Weber has not figured the supracallosal vestige 

 of the hippocampus, but represented it, together with the corpus callosum, as one 

 structure. 



In Orycteropus I have found that the corpus callosum measures 21 mm. in length and 

 2 mm. in thickness in a hemisphere whose maximum length is 60 mm. 



Although the corpus callosum becomes reduced in some families, especially in the 

 Armadillos, to very diminutive proportions, it is very misleading to state as a general rule 

 that the corpus callosum is small in the Edentata. To appreciate the full significance 



* Op. fit. pi. iv. fig. 4. 



t O^). cit. vol. XXV. fig. 13. 



J Max Weber, o^j. cit. tab. ix. fig. 69. 



§ Pouchet, 0/1. cit. pi. iv. fig. 10. 



42* 



