386 Dli. G. ELLIOT SMITH ON 



The effect of this is that iu the Carnivore there is an early and most pronounced 

 tendency in the suprasylvian sukius to assume an arcuate form, whereas in the Ungu- 

 late the correhpondiny fissure is horizontal uutii, in a late stage in certain Ungulates, the 

 perfection of the Sylvian fissure produces a secondary arching in the suprasylvian 

 fissure. There is also, as we have already had occasion to remark, a correlative change 

 in the early Carnivore and early Ungulate type of Sylvian fissure. 



Among certain mammals, such as the Rodents, there is an ill-defined tendency toward 

 a development along the Carnivore line of evolution, but it is never very pronounced. 

 At tlie same time we find in some Rodents, as for instance Lepus, a decided caudal 

 dovvngrowth of the pallium which is not unlike the condition in Tamandua. Among 

 other Rodents * we find evidences of a sagittal sulcus, a supraorbital, and occasionally a 

 fossa Sylcil, which in a vague manner suggest a tendency similar to that exhibited in 

 the Carnivore's brain. The Chiroptera present a type of brain similar to the Rodentia 

 with even fewer indications of their affinities, and they both gradually merge into 

 the generalized type of the Insectivora, which gives no indication of the peculiar 

 specializations of the higher groups. When we consider that the Carnivore type is so 

 distinctly marked ofl' Irom that of all other groups of mammals, and find in an 

 enigmatical lamily of mammals such as the Ant-eaters an exact reproduction of all 

 the salient features of this distinct type f, we are justified, I think, in attaching some 

 taxonomic value to the resemblance. 



If we admit that such a genetic relationship does exist, we must make the further 

 concession that the Aut-eater stock branched oh' in all probability from the early Ungui- 

 culate stock at a period subsequent to the splitting off of the Condylarthra or primitive 

 Ungulata. Although the brain of the Ant-eater is far inferior to that of the Carnivore, 

 it is immeasurably superior to tliat of the primitive Creodont. Arguing from the 

 evidence afi'urded by the brain, we might surmise that the Ant-eaters branched ofi* at 

 an early epoch from the primitive Carnivore stock at a time when the peculiar and 

 distinctive tendencies of pallial development had been fully determined. But Avhile 

 the- Carnivores, leading an open life of free competition, have in the keen struggle for 

 existence developed iu a high degree the organ which permits them to successfully 

 maintain the struggle, the Ant-eaters, on the other hand, have become peculiarly 

 specialized to a particular kind of life in which their safety is assui-ed, not by an exercise 

 of a highly developed brain, but by leading a life of seclusion. They pursue a prey which 

 does not call for that exercise of cunning and keen activity of muscle which alone can 

 make a Carnivore's life possible. 



According to the interesting palseontological investigations of Wortmau 1, the early 

 Eocene deposits of North America contain a series of peculiar extinct mammals, 

 Ijeginning from the earliest Puerco and continuing uninterruptedly into the Bridger, 

 which seeju to throw an interesting light upon the ancestry of the American Edentates. 



* Cf. F. E. Beddard, Proc. Zool. Soc. London, 1S92, p. 596. 

 t Except for the crucial sulcus, -which we have discussed elsewhere. 



+ J. L. "Wortmau, " The Gauodouta aud their Eelatiouship to the Edentata," Bulletin of the American Museum 

 of Natural History, vol. is. art. vi. pp. 50-110, 1897. 



