320 PEOF. G. ELLIOT SMITH OX THE 



of the sulci (and the organ in which they occur) to one circumscribed group of mammals ; 

 and, so as not to also narrow tbe scope of this discussion by so doing, I have freely 

 introduced comparative data, which serve to indicate the behaviour of each individual 

 sulcus in the whole Mammalian class. 



Tlic brain of tlie Lemurs lias been selected as the aptest expression of these require- 

 ments. I can best explain this by anticipating some of tbe conclusions of this research. 

 Tlie features of the Prosimian brain become really intelligible only on the supposition 

 that the Lemurs have advanced a considerable distance in the main stream of the 

 evolution of the Primates and have then retrograded; among other manifestations of 

 this retrogressive process many interesting phases of the disintegration of the cerebral 

 sulci are exhibited, so that it becomes possible to recognize the constituent elements of 

 many compound sulci in the Primates, and so the more readily to compare them with the 

 lurrows found in other mammals. 



My choice of the Lemurs was further confirmed by other considerations of a very 

 diiferent nature. The opportunity of examining a much more representative collection 

 of Prosimian brains ihan had previously fiilleu to the lot of any one observer, and the 

 imique facilities for studying the brain-form of the extinct Lemuroids, for which I am 

 indebted to the kindness of Dr. Forsyth jNIajor, were additional reasons for choosing the 

 brain of the Lemurs as the touchstone on which to test the hypotheses suggested by a 

 study of the brain <-.f other mammals. Moreover, the present state of our knowledge of 

 the mammalian brain is so unsatisfactory, that no apology would be necessary for 

 discussing its apparently obvious features in any Order, and least of all in the 

 enigmatical family of Lemurs ; for in no group of mammals is accurate knowledge 

 of the brain more urgently wanted than in the latter. The voluminous literature of the 

 Prosimian brain is jiarticularly barren so far as exact and authentic statements of fact 

 are concerned, and unduly rich in the grossest inaccuracies. 



The foregoing statement of the object of these notes will explain their nature and 

 scope. They do not pretend to be a monograph on the Prosimian brain, but are rather 

 an account of the more variable features of the mammalian brain, as these are exhibited 

 in the Lemurs. I have deemed it advisable, if for no other purpose than to give some 

 idea of the " setting " of the j^attern of the cerebral convolutions, to give a brief account 

 of the outstanding features of the brain as a whole. The morphology of the mammalian 

 cerebellum is incidentally discussed also. 



In attempting to settle such an essentially morphological problem as the search after 

 a fundamental plan underlying the apparently heterogeneous maze of cerebral sulci 

 found in the diflferent Orders, the observer is afforded an excellent opportunity of 

 appreciating at their true worth the factors which disguise the common plan. The 

 value of the evidence of the brain as an indication of the closeness of the bonds of 

 affinity between the Lemurs and other mammals hence falls not unnaturally within 

 the scope of this study. 



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