THE BRAIN I\ THE EDENTATA. 385 



It is strange that in animals with such a small and insignificant pallium, which is not 

 of sufficient extent to produce a complete rhinal fissure, we should find representatives of 

 what we must regard as the supraorbital (/3) and sometimes also the suprasylvian (S) 

 sulcus. So far as we are at present capable of judging with our limited knowledge of 

 the factors of pallial growth, there is little, if any, mechanical demand for any such sulci. 

 If this be so, these fissures must have been inherited from ancestors of the Armadillos 

 which possessed a more extensive pallium with fully-formed supraorbital and supra- 

 sylvian sulci. 



The evidence of anatomy and palaeontology, which has been carefully summed up 

 by Sir William Flower*, clearly points to the undoubted kinship of the Ant-eaters, 

 Sloths, and Armadillos. There is nothing in the evidence of the brain which does not 

 thoroughly harmonize with this view. Ilyrmecophafja exhibits a close resemblance 

 to the brain of the Carnivora which we have already examined in detail. When we take 

 into consideration the multiplicity of factors which are moulding the pallium into such 

 varied forms in different groups of mammals, it is difficult to explain the resemblance 

 between the pallial configuration of the Great Ant-eater and that which prevails in the 

 great group of Unguiculata, as other than the expression of a genetic relationship, and 

 not of fortuitous similarity. 



We equally find in Bracli/pt(s, but to a less marked degree in Choloepus, signs of 

 conformity to the Carnivore type of brain. 



In the case of the Dasypodldce, the rudimentary sulci /3 and o may be the remains of 

 a similar pattern, but it is so fragmentary that from the evidence of the brain alone we 

 could not definitely locate these peculiar animals. 



In spite of the obvious differences which exist between the brain of the Carnivora and 

 that of the Ungulata, we find that among their most constant mori^hological features 

 there is a very considerable anaount of agreement, while other constant features coexist 

 to point the contrast. The arrangement of the supraorbital and sagittal sulci, and 

 to some extent the splenial sulcus, is so obviously homologous in the two types that we 

 cannot regard this fact in any other light than the expression of an ultimate genetic 

 relationship. If we trace the ancestry of the Ungulata and the Unguiculata back, we 

 ultimately reach, according to the evidence of recent palaeontology, a common Creodont 

 stock, from which at the dawn of the Eocene the Condylarthrous progenitors of the 

 modern Ungulata diverged from the forerunners of the Carnivora t- It is highly probable 

 that in the simj^le brains of these primitive Creodonta those tendencies of growth 

 were already impressed which equally manifest themselves in the pallium of the two 

 diverging groups which spring from this common stock. 



The divergence of these two stocks is manifested in the contrast between other 

 features of the pallium in the two groups. The pallium in the Carnivore at a very early 

 epoch bulges downward posteriorly, while this tendency is wanting in the Ungulata. 



* W. H. Flower, " On the ilutual Affiuities of the Animals composing the Order Edentata," Proe. Zool. Soc. 

 London, I881!, pp. 358-367. 



t W. D. Matthew, " A Revision of the Puerco Fauna," Bulletin of the American Museum of Natural History, 

 vol. is. 1897, p. 293, Condylarthni . 



