CHAP. IV] THE GENERAL ANATOMY OF THE TARSII 113 



Of the marginal pallium, the most distinctive feature is 

 provided by the direct passage of the gyrus dentatus towards 

 the splenium of the corpus callosum, no sub-splenial flexure being 

 present. In no Lemur or Ape is this arrangement found, and for 

 a comparable disposition of parts, the lowly brain of the Sloth 

 must be examined. The determining factor is the small extent 

 (backwards) of the corpus callosum, and the limitation of growth 

 in this commissure stamps the brain of Tarsius as one of the most 

 primitive among those of Eutherian mammals. 



The general form of the neopallium has been described above. 

 The deep orbital excavation is indicative of the enormous eyes. 

 With these is to be associated the remarkable occipital pro- 

 longation of the neopallium behind the corpus callosum, and over 

 the cerebellum. In this prolongation an extensive posterior cornu 



Fig. 63. Tarsius spectrum. Mesial aspect of the cerebral hemisphere. (After 

 Elliot Smith.) x 4. 



of the lateral ventricle is situated. As might be anticipated, the 

 area striata (visual area) of the cortex is extensive. The histo- 

 logical features of this area, and indeed all the features just 

 enumerated as distinctive of the occipital region, separate Tarsius 

 from the Lemuroidea, bringing it at the same time into relation 

 with the lower Anthropoidea. 



The various areas of the neopallial cortex are exhibited in 

 a diagram (Fig. 64) based on a sketch which I owe to the kindness 

 of Professor Elliot Smith. To the same authority I am indebted 

 for sketches from which Figs. 65 and QQ have been prepared. 

 These represent two types of brain in the Insectivora, and taken 

 together with Fig. 64, they provide a graphic illustration of the 

 evolution of the neopallium. But it is to be understood clearly 

 that the indications are of a general nature only, and that the 

 charts are not necessarily precise in detail. 



d. m. 8 



