NERVOUS SYSTEM. VRRTKBRATA. 487 



D. 649. That of the right side, however, probably giv<> t h- 

 clue to the interpretation of all the other brains. A very 

 well-developed inferior transverse sulcus appears to unit.- 

 (superficially) the Sylvian fissure to a very exto'ii-iv.- 

 arcuate sulcus, which has now altogether dissociated itself 

 from the sulcus rectos, and has become so far extended 

 mesially as to usurp the place of the anterior part of tin- 

 superior frontal sulcus. The sulcus recttis also is now 

 represented by two irregularly branched snlci, the posterior 

 of which is in other brains joined to the arcuate. 



The lower end of the fronto-orbital sulcus bends back- 

 ward into the Sylvian fissure in a peculiar manner on both 

 hemispheres, and particularly so on the left side. 



The occipital operculum is much better developed in this 

 than in most Orang's brains, so as to almost completely 

 cover the submerged arcus occipitalis (which has been 

 exposed on the left hemisphere by drawing apart the lips 

 of the Simian sulcus). 



The calcarine sulcus is unbranched. In the right hemi- 

 sphere there is an extensive accessory calloso-marginal 

 sulcus parallel to the main sulcus, below which it is placed. 



A small paraflocculus may be seen emerging at the outer 

 side of the flocculus. 



D. 652. The brain of an Orang-Outang (Simla aatyrus). 



In spite of the large number of Orang's brains in this 

 Collection, this small and damaged specimen has been 

 added because it exhibits some unusual features. 



The exposed part of the superior limiting (Marchand's 

 " opercular ") sulcus is so diminutive that the anterior 

 insular region is hardly more distinctly delimited than in 

 the larger Cercopithecidse. 



The left fronto-orbital sulcus is small, whereas the right 

 is long and Y-shaped. 



There is an unusually complete superior frontal sulcus in 

 both hemispheres. 



It is peculiar how frequent is the union of the inferior 

 transverse ("diagonal," according to Cunningham) and 

 arcuate sulci on the right, and not on the left hemisphere. 

 On the left hemisphere the sulci arcuatus and rectus 



arc 



