378 



rated from the flocculus by a definite fissura floccularis and forms a 

 large widely projecting fist-shaped mass consisting of four or five 

 plump folia. 



In a very large number of small mammals including most of the 

 other Marsupialia, all the Chiroptera, the Dasypodidae, most of the 

 Kodentia and the smallest Primates (Tarsius, Microcebus) a 

 further series of similar changes occur in the lobus medius. The 

 lateral parts (or "alae", as I shall call them) become marked off from 

 the mesial part (vermis) by the appearance of a triangular area of 

 exposed medullary substance in the dorsal part of the lobe (Fig. 18). 

 The postpteroid area tends to project upward and forward as a tongue- 

 like process overlapping the pteroid area : as the result the postpteroid 

 fissure in most small mammals is placed on the anterior surface of 

 the organ. Both the vermis and the posterior surface of the para- 

 vermis (i. e. the postpteroid and parapyramidal areas) become divided 

 into folia by numerous transverse fissures (Fig. 18). The pteroid area 

 is at first (e. g. in Dasyurus) a simple, narrow folium bounded by 

 very deeply-incised postlunate and postpteroid fissures and overlapped 

 in great part by long, tongue-shaped processes of the lunate and post- 

 pteroid areas respectively in front and behind. 



In all Orders anomalies are produced by irregular modes of con- 

 fluence of the various fissural elements. Thus I have seen in the 

 brain of a pouch-specimen ofTrichosurus (a genus in which the 

 normal arrangement [vide op. cit. infra, 7] is usually found) the fissura 

 secunda joining the parafloccular fissures (Fig. 19), so that the dorsal 

 limb of the paraflocculus is joined to the vermis by a band ("copula 



Pars suprapyr. 



Fiss. suprapyr. 



Area medullaris 



i Pyraniis 



Area 

 postpter 



Paraflocc. 

 Lobulus 

 petrosus 



Parafi; JL 

 Flocc. x^f 



Fiss. 



Floe. Nodulus 



Uvula 



Lobus 

 flocc. 



Fiss 

 secunda 



19. 



Nodu- Uvula 

 lus 



Fig. 18. Fig. 



Fig. 18. The caudal aspect of the cerebellum of Dasyurus viverrin us, the 

 left side diagrammatically represented, the right side ad naturam. X 3- 



Fig. 19. The caudal aspect of the abnormal cerebellum of a pouch - specimen of 

 Trichosurus vulpecula (total body-length 14 cm). X 8 - 



