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"fissura postlunata". It will subsequently be shown that these fissures, 

 when (as sometimes happens) they become confluent on the vermis, 

 represent the furrow commonly called sulcus (vel fissura) postclivalis 

 (cacuminal sulcus [Stroud]; erroneonsly called "sulcus horizontalis 

 magnus" by Kuithan [op. cit. 1, Fig. 21, p. 34]). 



In the vast majority of mammals (excluding only most Ungulata, 

 Sirenia and the smallest mammals) the region immediately behind the 

 fissura lunata assumes a wedge-shaped form and becomes split up into 

 a feather-like arrangement of folia (vide Figs. 23, 24 and 25) : I shall 

 call it the "area pteroidea" (titeqov — a feather). 



In most brains the caudal limit of this area is indicated by a 

 furrow which I shall call "postpteroidea" : it will be seen later that 

 this relatively unimportant furrow represents the fissura (sulcus) 

 horizontalis magna (the peduncular sulcus of Wilder). In some 

 brains this fissure is absent when the postlunar, suprapyramidal and 

 parapyramidal fissures are present; and in all of the cerebella the 

 developmental history of which I have studied (those of Dasyurus, 

 Trichosurus, Macropus, Homo inter alia) this fissure (to 

 which such undue importance is usually attached) makes its appearance 

 after the above-mentioned three furrows, and long after the fundamental 

 fissurae flocculi, paraflocculi, postnodularis, prima and secunda have 

 developed. Stroud has already demonstrated this in the case of 

 the brain of Homo (op. cit. 3) ; Kuithan, however, failed to recognise 

 this important fact, because he mistook the more precocious fissura 

 postlunata for the fissura postpteroidea (sulcus horizontalis magnus). 



That part of the middle lobe which is placed on the caudal side 

 of the fissura postpteroidea I have called the paravermis. It is sub- 

 divided by means of the parapyramidal fissure into a dorsal part — 

 area postpteroidea — and a ventral part — area parapyramidalis. 

 The term paravermis is introduced as a purely descriptive term for a 

 very obtrusive feature of the cerebellum in most mammals. In the 

 natural subdivision it is invariably split into the postpteroid and the 

 parapyramidal areas and the latter again in the Primates becomes sub- 

 divided into distinct "biventral" and "tonsillar" parts. So that in 

 various groups of mammals some of these terms are more convenient 

 than in others and vice versa. 



The simplest mammalian cerebellum, that of the small Marsupial 

 Mole (Notoryctes typhlops, Stirling), represents a stage through 

 which the more complex organ of all other mammals passes at an 

 early stage in its developmental history. This organ with its fully- 

 developed histological structure affords a very useful demonstration 



