384 DE. G. ELLIOT SMITH ON 



In Tamandna, as a resvilt of the elongated form of the head necessary for an Ant-eater, 

 the brain has plenty of room to expand, and hence its cortex does not become folded 

 like that of the Slotlis. 



If it be true that the surface of the pallium of Bradijims thus becomes folded in 

 accordance with mechanical principles, it is somewhat remarkable that the arrangement 

 of its sulci should follow a plan whicli is obyionsly the expression of an inherited tendency. 

 That this does take place there can be no doubt, for when we examine a large series of 

 mammalian brains we are surprised to iind in organs of the most variable shapes con- 

 vincing evidence that the arrangement of the sulci has been determined by some principle 

 other than the purely mechanical factor which may have been the exciting cause of 

 their development. 



Max Weber records a brain weighing 11-3 gr. in a DasyptLs sexcinchis c? of 2567 gr. 

 There is a most decided fall both in tlie absolute and relative size of this brain wdien 

 compared with those of tlie Sloths and Ant-eaters. Nor does a comparison of this record 

 with those of members of the Rodentia, Chiroptera, or even Marsupialia, serve to 

 brighten or place in a better light the degradation of the Armadillo. Por in the 

 Marsupial Trichosuriis we find the record of a brain of the same size as that of Dasjjpus 

 in an animal of merely 1724 gr. But at the same time it is only right to add that a 

 Didelphys of BiSO gr. has a brain of merely 6"5 gr. 



I think there is ample reason for hesitation before consigning the Armadillos to a 

 lowly place, even if we admit, as is not improbable, that this single record is typical of 

 the family. 



In our consideration of the factors which may modify the size of the pallium we have 

 already pointed out that the decadence or diminished acuteness of any sense-organ may 

 exercise a marked effect upon the size of the pallium in those mammals in which the 

 " areas of association " are not yet definitely established. In the consideration of the 

 mesencephalon we have already had evidence to demonstrate that the visual acuteness of the 

 Armadillos is on the wane. When we consider how large a share visual representation 

 must take in the primitive pallium, we must admit that this is a potent factor in modifying 

 its size. In addition to this, it is hardly to be believed that tactile impressions are of much 

 importance, or find any scope for their exercise, in an animal encased in armour. The 

 tendency of recent research is to recognize in the optic thalamus a station wiiere not 

 only the visual but also the general tactile path receives a relay on its way to the 

 pallium. If this be so, w^e may perhaps be able to understand why the optic thalamus 

 is reduced to such exceedingly diminutive proportions in the Armadillos. If we admit 

 that the visual and tactile senses have a diminished importance in the Armadillos, I 

 think that there is in this fact an ample reason for the diminutive size of the pallium. 

 Pouchet tells us that the brain of Chlamydo'phorus is much larger than that of the Mole 

 ( TuIjm). If this be a fact, it may be of value as evidence of the superiority of the 

 Ai-madillo over the Insectivore. 



We must regard the i\rmadillos as the descendants of mammals with a higher degree 

 of visual and tactile acuteness, and a much more extensive pallial representation of these 

 senses than they at present possess. 



