112 THE GENERAL ANATOMY OF THE TARSII [SECT. A 



preliminary considerations are to be borne in mind as in the case 

 of the Lemuroidea (v. supra, p. 85). 



(i) The cerebral characters undoubtedly include some which 

 may be described without hesitation as primitive. It is note- 

 worthy that in Tarsius such characters are found to be related to 

 the commissures of the hemispheres. Of these, the corpus callosum 

 provides the most striking example, for its extent in an antero- 

 posterior direction is remarkably small. The cerebellum also falls 

 within this category. 



(ii) Primitive or pseudo-primitive features accountable to 

 processes of reversion or degeneration are not generally recog- 

 nized. 



(iii) The large size of the eyes, consequent upon the adapta- 

 tion of Tarsius to nocturnal habits, has produced a most marked 

 effect on the general form and proportions of the cerebrum, both 

 directly and indirectly. 



(iv) Tarsius is a very small mammal, and as such it provides 

 evidence confirmatory of the general rule that in the smallest 

 forms, the complexity of cerebral convolutions is far less than in 

 larger representatives. 



The details now to be added will involve further elaboration 

 of these general principles. The cerebrum of Tarsius (Figs. 60 — 

 64 incl.) is remarkable in form and proportions. Viewed from 

 above it is broader than it is long, and the surface is devoid of 

 all sulci save a slight impression (Fig. 60, ss) identified with the 

 S. suprasylvius. 



When examined from one side, the hemisphere (Fig. 60) is 

 marked in front by a deep and extensive fossa where it rests on 

 the orbit. The occipital end also bears an impression on its 

 ventral aspect where it extends over the cerebellum to a con- 

 siderable extent. 



The rhinencephalon comprises a small sessile olfactory bulb of 

 " triticeal " form, a short wide peduncle, a (relatively) small pyri- 

 form lobe, with a small tuberculum olfactorium. The rhinal 

 fissure is not usually distinguishable. On the whole, the rhinen- 

 cephalon stands mid-way between those of the Lemuroidea and 

 the Anthropoidea. 



