NERVOUS SYSTEM. VEBTEBBATA. 363 



By far the most significant feature of these brains of the 

 Aye-aye is the existence of a separate suprasylvian arc. 

 In the Carnivora and many other mammals (e. g. Bradypns) 

 the suprasylvian sulcus is joined to the postsylvian 

 (generally known as "posterior suprasylvian") to form 

 a " supra-sylvian arc." Such an arc is generally found in 

 the brain of Daubentonia, but in that of no other Primate. 

 In all the Lemurs and Apes the suprasylvian sulcus is 

 separated from the postsylvian (which is then called 

 " parallel " or " superior temporal ") sulcus ; and the 

 former then appears to be joined to the angle of the rhinal 

 fissure by means of a shallow depression, the nearest parallel 

 for which is to be sought in the sulcus erroneously called 

 " Sylvian fissure " in most mammals. The latter is not the 

 true Sylvian fissure, but a sulcus of no morphological 

 stability, which is probably produced as a kink in the 

 neopallium at the site of its bending. The true Sylvian 

 fissure is a peculiar complex of many elements, which is 

 seen in its perfect form only in the human brain. Its 

 fundamental constituent is the. suprasylvian sulcus, and in 

 some Lemurs the u Sylvian fissure " is the suprasylvian 

 sulcus, pure and simple. But in most Primates the dorsal lip 

 of the suprasylvian sulcus would seem to become opercular 

 and tends to overlap a depressed area which is also partly 

 covered by the forwardly extending posterior opercular 

 lip of the pseudosylvian sulcus. According to this hypo- 

 thesis, the suprasylvian sulcus of non-Primate mammals is 

 represented in the Primates by the superior limiting sulcus 

 of the "island of Reii," which is the fundamental 

 constituent of the complex known as the Sylvian fissure. 



The great importance attaching to the brain of Dauben- 

 tonia lies in the fact that the suprasylvian sulcus (which a 

 comparison at once shows to be identical with the Lemurine 

 " Sylvian fissure ") is not linked to the rhinal fissure, but is 

 joined in most cases to the postsylvian sulcus, as it is in the 

 Carnivora and many other mammals. An interesting parallel 

 phenomenon is found in the brain of the Great Anteater 

 (Myrmecopliaga jubata). In most cases the suprasylvian 

 sulcus of this creature is completely separated from the 

 postsylvian and joined by that suprarhinal kink, which may 



