166 



DE. G. ELLIOT SMITH ON THE BEAIN 



(see I, fig. 6, p. 330). Even in recent Lemurs of the same species these features are 

 subject to considerable variation, and it often happens that the fronto-orbital [diagonal] 

 sulcus is situated either partly or even wholly beyond the rim of the orbital depression. 

 In Lemur jullyi the orbital depression extends barely half the distance from the frontal 

 pole to the Sylvian fissure, and the fronto-orbital sulcus is placed on the oviter face of 

 the hemisphere 4 mm. behind the orbital margin (fig. 54). In these respects the brain 

 under consideration resembles those of the family Lorisinse. The orbital surface is 

 very small in these Lemuroids, and, although the fronto-orbital sulcus does not usually. 



Text-fig. 54. 

 s. intrapcLrieialis. 



AssSyh- s.limat,. 



si/tus lateralis. 



cereieiZunv. 



s. front, inf. -f- 



bidh.olf> 



s.orbitciUs. \ a.fr-orUo-orbitalis. 

 f.rhina/is- 



Diagram of the left lateral aspect of the brain of Lemur jullyi. Natural size. 



if indeed ever, properly develop in them, we know (from the distribution of the 

 claustrum and its relationship to the sulcus in other Lemurs — see i, fig. 60 «, p. 408) 

 exactly where it would make its appearance, and that is in a situation exactly coinciding 

 with the place actually occupied by the furrow in Lemur jullyi. In these respects 

 the extinct species exhibits what is probably the more primitive and common Prosimian 

 configuration, which the recent species have lost in varying degrees. It is specially 

 worthy of note that all of the extinct Lemuroids — Nesopithecus (fig. 60), Palceopro- 

 pitliecus (fig. 63), and Mesopropithecus (fig. 69) — resemble Lemur jullyi (fig. 54) and 

 the hypothetical primitive Prosimise in this respect. This is especially noteworthy in 

 the case of the brain of Mesopropithecus, because in all other respects it is an almost 

 exact replica of the organ in Indris. 



The form of the olfactory bulbs, the pyriform lobes, the rhinal fissures, and the 

 orbital, fronto-orbital [diagonal], inferior frontal [coronal], Sylvian, parallel [superior 

 temporal or post-Sylvian], and intraparietal [lateral] sulci calls for no detailed account, 

 since all of these features so closely resemble those of the recent Lemurs, which 1 have 

 already described (i). 



The fronto-orbital [diagonal] sulcus is exceptionally deep and cleanly cut and, 



