TARSIUS SPECTRUM 97 



THE OPTIC CHIASM 



The optic chiasm is Hat and broad and gives the impression of generally 

 greater thickness than in other forms, due to the fact that almost all of the 

 optic fibers undergo decussation. Very few optic fibers in tarsius are uncrossed. 

 The interpeduncular space is small, bounded by feebly developed cerebral 

 peduncles, while the temporal lobes are broad and Hat, each filling a more or 

 less irrcguhir quadrate area in the lateral portion of the middle fossa. 



THE VENTRICLES AND THE VISUAL CORTEX 



The ventricular system of the hemispheres is particularly significant, 

 inasmuch as the lateral ventricle develops a posterior horn extending into the 

 occipital region, which is not the case in any of the lemurs. The ventricular 

 extension of the olfactory peduncle characteristic of many mammals is, 

 however, being obliterated. The visual cortex of the cerebral hemisphere 

 shows a marked increase as compared with lower mammals and even the 

 lemurs. It is easily detected by the naked eye and occupies nearly one-third 

 of the entire neopallium. 



THE CEREBELLUM 



The cerebellum is notable as indicating those lateral expansions which 

 in higher primates become the most important part of the organ, namely, 

 the lateral cerebellar lobes. Tarsius in many respects is an excellent proto- 

 type in most simple terms for the subsequent extensive development of the 

 primate cerebellum. Its tentorial surface lies at an angle of about 70'^ with 

 the axis of the stem, thus showing the early tendencies which eventually 

 carry this surface more nearly into the horizontal. The occipital lobe covers 

 most of the tentorial surface which consists largely of the superior \-ermaI 



