NERVOUS SYSTEM. VERTEBRATA. 171 



is a complex of two (and often three) new element* ; it makes its 

 appearance for the first time in the Anthropoidea in the region 

 between the phylogenetically old calcarine and intruparietal sulei, 

 which are the common heritage of the Meta- and Eutheria. This 

 account will explain the extreme variability of the parieto-occipitul 

 sulci in the human brain. 



There is yet another remnant in the Primate-brain of the calcarine- 

 intercalary junction (which occurs in so many mammals) in the form 

 of a short sulcus above and behind the splenium, which I have called 

 " compensatory " (instead of Broca's misleading title " postlimbic "). 



The Sylviau fissure in its complete form is found only in the 

 human brain, and even in Man it is often imperfect. It is really a 

 great cleft upon the ventro- lateral aspect of the hemisphere formed 

 by the meeting of the peripheral opercular lips of three sulci, 

 which are quite distinct in origin and in their phylogenetic history. 

 The most stable of these three sulci, and therefore that which takes 

 the chief share in the development of the Sylvian fissure, is that called 

 " suprasylvian " iri most mammals. The second is an unstable sulcus 

 analogous to the pseudosylvian sulcus (that which is commonly called 

 the " Sylvian fissure ") of the Carnivora and many other mammals. 

 And the third sulcus is the fronto-orbital. 



The suprasylvian sulcus is one of ths most primitive and constant 

 in the Mammalian series. It is the earliest neopallial sulcus to make 

 its appearance on the external surface of the hemisphere in the course 

 of the development of the Carnivore, Ungulate, and (according to the 

 old observations of Pouchet) Edentate brain, synchronising in this 

 respect with the calcarine sulcus on the mesial surface. Even if its 

 identification is not altogether sure in the Marsupialia (see the 

 accounts of Thylacinus, Macropus, and Phascolomys}, we know that it 

 is a most stable sulcus in the Edentata, Ilodentia, Carnivora, and 

 Ungulata. In many Mammals it is joined to the less stable post- 

 sylvian (" posterior suprasylvian " of most writers) sulcus, which 

 we call " parallel " in the Anthropoidea. In the Great Anteater, 

 however, it usually becomes separated from the latter and joined 

 to a pseudosylvian sulcus to form a Sylvian fissure, not unlike 

 that found in the Lemuroidea. It is significant that in the 

 only case in six hemispheres of Myrmecophaya where this junction 

 does not take place, it should also happen that the supra- 

 sylvian sulcus is joined to the postsylvian, as in the Carnivora. In 

 Daubentonia the suprasylvian sulcus is always separate from the 

 pseudosylvian, and is generally joined to the postsylvian sulcus. 

 the Family Lemuridee the suprasylvian sulcus is always (or practically 



