392 PROF. G. ELLIOT SMITH OX THE 



Cunningham has said that " we arc not in a position at present to offer an opinion . . . 

 upon the statement that the calcariae fissure is also developed in brains below the 

 Primates " *. Pive years later he stated that, " except in the case of certain of the main 

 furrows {c g. Sylvian, hippocampal), it is very questionable indeed if there is any 

 homological correspondence between the sulci of a primate brain and the sulci of a 

 quadrupedal brain." In spite of all the research in this field since these quoted passages 

 were written, Cunningham has recently reafhrmed his unaltered belief in his view 

 in these words : — "We now know that the primate cerebrum was not only distinguished 

 from that of all lower mammals by the possession of a distinct occipital lobe, but also by 

 having imprinted on its surface a convolutionary design which, in all but a few 

 fundamental details, was different from that of any other order of mammals " f . 



What is this occipital lobe, w hich is so distinctive of the Primates ? Cunningham 

 himself does not tell us what he means by the expression. If it is merely the caudal 

 prolongation of the hemisphere above the cerebellum, then many large Carnivoi*es have 

 an equal or perhaps better right to be regarded as Primates than some of the Lemurs ; 

 and if it is the posterior cornu which is the diagnostic sign, then the Lemurs cannot be 

 regarded as Primates, whereas the Seals, the Camel, and some Cetacea are to be classed 

 along with the Apes. If, however, it is the calcarine sulcus which, to quote Turner, 

 " determines the presence of an occipital lobe," how can we draw a line of demarcation 

 in respect to this feature between the Primates and other mammals? So far as I am 

 aware, these arc the only possible criteria of an " occipital lobe," and none of them, 

 either separately or in conjunction, can be regarded as exclusively distinctive of 

 the Primates. 



If we refuse to admit the homology of the cilcarine sulcus of the Primates and 

 the retrosplenial part of the splenial sulcus of other mammals, we have a far more 

 ditiicult problem to solve. For an explanation is then needed of the reasons for 

 regarding as different two sidci (in different groups of mammals) presenting identical 

 relations to the lateral ventricle and to the neighbouring brain-regions, a similarly 

 precocious appearance in ontogeny, and a constancy under varying conditions in mammals 

 which have widely diverged from the primitive stock. Why should we suppose that the 

 splenial sulcus, which is the most constant and most precocious neopallial furrow in the 

 mesial wall of the hemisphere in the Marsupialia, Cliiroptera, Edentata, Carnivoiu, 

 Lngulata, and Cetacea, fails to develop in the Primates, and that another and a different 

 furrow develops in the Primates in a position, which exactlij eot'respoiids to that occupied 

 by the splenial in other mammals and at the same epoch in development ? Such a 

 phenomenon is utterly inconceivable. The calairine and the retrosplenial part of the 

 splenial sulci are certainly identical. 



But, it may be argued, the calcarine sulcus is an independent furrow, whereas the 

 " splenial " is prolong(>d into a supracallosal course — the intercalary sulcus. Put in the 

 Myrmecophagidai, Bradypodidai, and Manida) the calcarine is not joined to the inter- 



* " Complete Fissures of the Human Cerebrum," Journal of Anatomj' and Physiology, vol. xxiv. p. 343. 

 t Presidential Address, Section H, Anthropology, British .issoeiation, September 1901. 



