108 MR. FLOWER ON THE BRAIN OF THE JAVAN LORIS. 



A second character by which the Lemurs are distinguished from the Monkeys is the 

 large size of the olfactory lobes : but in these portions of the encephalic mass a gradual 

 increase may be perceived from the higher to the lower Quadrumana ; and they project 

 in front of the cerebral hemispheres in all the Platyrhini, and even in the greater 

 number of the Old World Apes. In the large majority of Mammals the base of these 

 lobes extends backwards to the under surface of the temporal lobe, obliterating the 

 lower part of the fissure of Sylvius ; whereas in the true Apes, and in Man, their con- 

 nexion with the cerebral hemisphere is chiefly- with the anterior lobe and the bottom of 

 the fissure itself. In this respect, as well as in the size of the lobes, Stenops and Lemur 

 hold an intermediate position between the two groups, more nearly approaching the 

 higher than the lower type. 



Another most distinctive characteristic of the primatial brain is the possession of a 

 complete Sylvian fissure. Although the presence of this important sulcus is not 

 recognized by some anatomists in the Mammalia generally, it exists almost throughout 

 the series, but in a rudimentary condition, the part which remains corresponding to 

 the middle portion of the fissure when completely developed. Concealed by the lips 

 of the Sylvian fissure is the median lobe — so well marked and even complex in Man, 

 simpler and smaller, but still distinct, throughout the greater part of the Monkey series, 

 but lost in the diminutive Marmoset, recognizable, however, in the Lemur, not dis- 

 tinctly traceable in Stenops, absent in all other Mammalia. Next to the fissure of 

 Sylvius, the most characteristic Simian sulcus on the outer surface of the hemisphere 

 is the one placed behind and parallel to it — the antero-temporal, the last that disappears 

 as the size of the brain, and attendant amount of surface-involution, decreases. In the 

 presence of this sulcus both Stenops and Lemur perfectly agree with the type. After 

 this the most persistent fissure on the outer face appears to be the one bounding the 

 upper border of the angular gyrus ; this also exists in Lemur, but is not seen on the 

 smaller hemisphere of Stenops. 



But it is perhaps the sulci of the inner face of the hemisphere that are most cha- 

 racteristic of the Primates, and offer the most striking differential features from the 

 other Mammalia. Here, too, the Lemuridae follow strictly the higher type. That 

 essentially primatial sulcus, the calcariue, which persists deeply marked in the little 

 Hapale iacchus, when every other trace of fissure, except the Sylvian, is gone, is equally 

 well developed in both Lemur and Stenops. The calloso-marginal is also well marked, 

 but a fissure somewhat corresponding to this is found throughout the Mammalia. 



In order to make a comparison of the brain of the Lemuridae with those of the 

 higher Quadrumana more perfect, brains of somewhat similar size in the two groups 

 should be selected ; and in reference to such a comparison, as well as on other grounds, 

 it is to be regretted that we are not yet sufficiently acquainted with the cerebral 

 organization of many of the Platyrhine Apes ; but among those that are known there 

 are two which, in general arrangement of sulci, present great resemblance to Lemur 



