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of the fundamental plan of the mammalian cerebellum. That the 

 cerebellum of Notoryctes is really a primitive (and not a retrograde) 

 type is shown by its close resemblance to that of Perameles, the 

 most generalised mammal known to us: but, by reason of its much 

 smaller size, the cerebellum of Notoryctes is much simpler even 

 than that of Perameles and lends itself better to histological 

 investigation. In no respect is the pro-mammalian character of 

 Perameles more strikingly shown than in the structure of its cere- 

 bellum: the contrast between the simple organ of the Peramelidae 

 (and Notoryctes) and the much more complex organ of the 

 Dasyuridae and the other Polyprotodontia is a most striking testimony 

 of the generalised structure of Perameles, which is also shown by 

 the other regions of the brain, the genital organs and placenta 

 (J. P. Hill) and, in fact, by all parts of the body. Wherefore, in 

 taking Notoryctes and Perameles as our basal types, we are 

 dealing with undoubtedly primitive forms. 



In mesial sagittal section the cerebellum of Notoryctes is sub- 

 divided by means of three fissures into four simple leaves of unequal 

 size (Fig. 5). Comparison of a series of mammalian cerebella re- 

 presentative of every family and most genera has demonstrated that 

 the two small leaves on the ventro-caudal aspect undoubtely represent 

 the nodulus and uvula (of the human brain): and the furrow separ- 

 ating them the one from the other is the fissura postnodularis 1 ). If 

 we group these two folia together as a lobus posticus (bounded on 

 its dorsal side by the fissura secunda) the rest of the organ shown in 

 the section falls naturally into anterior and middle lobes separated 

 the one from the other by the deep fissura prima. 



The lobus anticus (Fig. 12) is a simple, plain, transverse hemi- 

 spherical leaf, which is placed vertically in a depression on the 

 cephalic aspect of the larger hemispherical lobus medius 2 ). Each 



1) Morphologically this fissure is the anterior (cephalic) boundary 

 of the nodulus, as is seen in the earliest foetal stages (Fig. 3), and 

 ought strictly to be called "praenodularis", but in all adult cerebella it 

 lies on the caudal side of the nodulus, so that the term "postnodularis" 

 may be retained. 



2) In my first memoir on this subject (4) I called it "lobus cen- 

 tralis" but subsequently substituted the name "medius" (7), lest con- 

 fusion with the "lobulus centralis" of Human Anatomy might arise. 

 Perhaps the term "intermedius" would be more correct, but the term 

 "medius" is not wholly inappropriate and has the merit of brevity. A 

 precedent for such usage is afforded in the nomenclature of the musculi 

 scaleni, anticus, medius and posticus. 



