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VII. The Brain in the Edentata. By G. Elliot Smith, 3I..D. (Sydnetj), St. Johrs 

 College, Cambridge. {Communicated Ity Prof. G. B. Howes, F.R.S., Sec. Linn. Soc.) 



(With 36 Illustrations in the Text.) 



AUG 29 '^^^- Eead 7th April, 1898. 



Introduction. 



The interest which attaches to the study of the brain in any large group of animals is 

 considerably accentuated in the case of such an enigmatical order of mammals as that 

 discussed in this communication. Two aspects of this many-sided interest must appeal to 

 us very forcibly during the investigation of the strange assemblage of mammals which have 

 been gathered into one group under the name Edentata. For we may not unreasonahly 

 hope tbat the obscure problems of the interrelationships of the heterogeneous families 

 which compose this so-called " order," and the even more perplexing question of the 

 wider affinities to other groups of animals, may be elucidated by the evidence afforded 

 by the brain, which, as the master-organ of the body, must be allowed distinctive 

 importance. 



Then, again, the study of so many modifications of the mammalian type of 

 brain as we find within the limits of this group must exercise a considerable 

 influence upon the more strictly morphological problem of the " search alter the 

 fundamental lines in the structure of the brain," which, as Edinger has well said, is the 

 most important task of the brain-anatomist of the present day. This aspect of the 

 problem becomes all the more interesting in the case of a group of mammals like the 

 Edentata, wliich it is customary to regard as of lowly organization, when we remember 

 that changes of great significance, which must appeal equally to the systematist and the 

 morjjhologist, have taken place in the structure of the brain within the Mammalia. 

 For we find certain features in the cerebrum of the Monotremata and MarsupiaUa 

 which distinguish these groups clearly the one from the other and each from all the 

 Eutheria *. If the Edentata are as lowly organized as they are generally represented, 

 we might reasonably expect to find some definite evidence of this fact in those regions 

 of the brain which we know to have heeii so transformed at the birth of the Placentalia. 

 On the contrary, should the results of an examination prove that these recently modified 

 parts of the brain show the typiaxl features as fully developed as they are in such 

 Eutheria as the Ungulata or Carnivora, we might be justified in adopting this as 

 strong corroborative evidence in favour of the view that there is a much closer affinity 

 between the ordinary Eutheria and the Edentata than is usually supposed. 



* These features I have alread}' discussed before this Societj' (' The Origin of the Corpus Callosum, &c.,' 

 Traus. Linnean Society, 2nd series, Zoology, vol. vii. jjart 3, 1897), and elsewhere ; c/. ' Journal of Anatomy and 

 Physiology," vol. xsxii. pp. 23-58, 1897. 



SECOND SERIES. — ZOOLOGY, VOL. VII. 39 



