STRUCTURAL CULMINATION 947 



This lohation conc'spoiicls so nuich in detail throuf^lioul tin- orckr that tlirre 

 can he no doubt as to tlu' I'sscntial siinilanty existing m tliese niorpliological 

 leaturcs ol the central nerxous system. 



The CoN\OLUTio\ Ai I^A iTERN 01 Nil Pkim A IF. Bkaix. Thispattciii 

 coincides with striking consistencx . \\ here\er convolutions de\elop, their 

 general homologies ma\ be easil\ determined, if not b\ actual comparison 

 with the adult human brain, at least with some earlier tetal stages. 



Okbital and Occipital Conca\ hies ok the Primate Brain. The 

 two great conca\Tties on the basal surface ol the brain, known respectively 

 as tlu' orbital and the occii:)ital concavity, ma\- be ideiitilied as corresponding 

 leatures in all species. 



Ceri AiN Characi eristics OF THE Basal SiRFACE. Certain basal char- 

 acteristics are notablx similar. Ilius the ollactory bulb and its associated 

 structures ha\"e become much reduced in size as compared with the carni\()rcs 

 and ungulates. This is especially the case with the ollactor\ tracts which are 

 readily detachable trom the under surface of the bram as far back as the 

 trigomim oifactorium. In no instance does either the tract or tiie bulb 

 contain that ]:)r()Iongation of the xcntricular ca\'it\" common m lower mam- 

 mals. Another characteristic on the basal surface is the relation of tiie optic 

 ner\'es and optic tracts to tlu' chiasm m primates. The < ptic nerves approach 

 the chiasm and the tracts lea\c it at an angle much nearer ()0 degrees than 

 It is m an\ lower mammalian forms. When retracted the olfactory bulb 

 and tract usually reveal the beginning of a sniaH sulcus immediately in front 

 ol the trigonum oifactorium. 1 his is the sulcus olfactorius which more or less 

 completel\ bounds a gyre situated mesial to it, the gyrus rectus. The sulcus 

 olfactorius and the gyrus rectus occur in an incipient stage or fully developed 

 in all of the primates. 



Relation of the Cerebellar Hemispheres in the Primate Braix. 

 The relation of the cerebellum to the cerebral hemisphere is another identify- 



