THE BKAIN IN THE EDENTATA. 383 



that any excess in cortical area of the Dog over tlie Ant-eater nrnst be due to a richer 

 supply of iutrapallial elements, /. e. nerve-cells and tlieir resultant nerve-iibres which 

 associate the various sensory elements of the pallium the one with the other, as well as 

 with the cells whose axis-cylinder processes become projection-fibres and carry impulses 

 from the pallium to lower executive centres. In other words, the pallium of the Dog is 

 a more jjerfect machine thau tliat of the Ant-eater, in that it is more perfectly adjusted 

 to the higher psychical needs of the animal, and the actions of its various parts are better 

 co-ordinated by a richer association-system. 



It is instructive to notice that the growth of the Dog's pallium has been a general 

 expansion and not a local hypertrophy ; in other words, the association-elements cannot 

 be regarded as forming areas, as we might suppose from a too hasty application of 

 Elechsig's ideas, but that they pervade the whole pallium, and with their increase there 

 is a general pallial expansion. At the same time we had occasion to observe before that 

 it is not unlikely that a localized expansion may have taken place in the area where we 

 find the crucial sulcus in the Dog. In this region the mechanism which controls the 

 movements of the limbs is being rapidly elaborated, so that the Carnivore can execute 

 those complex, almost skilled, and rapid movements ujjon which its livelihood is 

 dependent. 



When we turn from the consideration of the Ant-eaters to the Sloths we at once 

 encounter some difficult problems. Por, while the pallium conforms to the Carnivore- 

 pattern in quite as marked a degree (at any rate in Bradypus) as it does in the Aitt- 

 eaters, it seems strange that in these small brains there should be so many sulci of such 

 a depth. Max Weber's tables contain a record of a Bradypiis tridactylus ? of 2130 gr. 

 weight with a brain weighing 16'5 gr. Thus this Sloth possesses a smaller brain thau 

 that of Tamandua, in spite of the fact that its body-weight is nearly double that of the 

 Ant-eater. And yet, while the pallium of the latter, as we have seen, is almost free from 

 sulci, the smaller pallium of the Three-toed Sloth is provided with a series of deep sulci 

 even more complete than those of the Great Ant-eater. The slightly larger brain of the 

 Two-toed Sloth has, in addition, a number of subsidiary sulci. It is quite possible that 

 the extreme shortness of the head in the Sloths may have the effect of limiting the 

 space for the brain, and that hence the expanding pallium becomes folded to adapt itself 

 to its limited space. 



Erom a careful comparison of the brains of Tamandua and Gijcloturm (so far as this 

 has been possible) with those of Uodeuts, we must admit that the Ant-eaters are certainly 

 not inferior to the E-odents in the size of the pallium. Nor is the quality of the pallium 

 inferior, if we may judge of its richness by the volume of commissural fibres and 

 projection-fibres proceeding from it. In all that is of greatest signifieance as regards the 

 superiority of a mammal, the Ant-eater is at least the equal of the Hodent. And yet it 

 is customary to relegate the former to a much lower status than the latter. The evidence 

 of the brain in the Great Ant-eater shows that this animal is not far removed from 

 the Carnivora, and the whole tendency of our examination of this group is to bring them 

 into very close relationship with such typical Eutheria as the Eodents and Carnivores. 



52* 



