428 



PROF. G. ELLIOT SMITH OX THE 



It will l)e seen that, iu spite of its smaller size, the cerebellum of the Insectivore is 

 slightly richer in furrows than the Marsupial, and that, in order to liud in tlie former 

 Order a cerebellar pattern of the same degree of richness as Femmeles exhibits, we must 

 select some small form such as IlacrosceUdes or Oryzornctes. 



It Avill be seen that the pattern found in Tarsius is much richer in fissnres than that 

 of either the Insectivora or the Marsupialia. And, if it be objected that this contrast 

 may be due to the smaller size of the organ in l^riuacem, the suggestion can be at once 

 i-efuted by showing that in the larger Insectivore Gymuura, in GaleopUJieeus, in many 

 Rodents like Lepus, and in the representatives of other Orders of a corresponding size, 

 there is a greater poverty of fissures than there is in Tarsius. This fact might be more 

 accurately stated by saying that the extent of the cerebellar cortex is determined, partly 

 bv the dimensions of the animal and partly by its zoological rank. 



Fi^.65. 

 yp. la. 



Fig. Co. — Ltmvr macaco. Dorsal as];ect of the cerebellum. x 2. 

 Fig. G6. — Gazdla dorcas. Left lateral aspect of t lie cerebellum. X 2. 



The mesial part of the cerebellum is divided into three regions by means of the deep 

 lissura prima, y//'., and by tl'.e shallower fissnra secunda,/s. (fig. 6A). The region iu front 

 of the tissura jn'ima (which is homologous Avith the so-called "preclival" tissvu'e) may be 

 called the anterior lobe, that between the fissnra prima and the fiss. secunda the central, 

 or, better, middle lobe; the third region being the posterior lobe. The anterior and 

 middle lobes may be quite simple vmdivided folia, as in Notoryctes, but the posterior 

 lobe is ah\ays subdivided into two lobules, which correspond to the parts called 

 " nodulus " and " uvula "' respectively in Human Anatomy. 



A comparisoai of a series of mammalian cerebella clearly sIioavs that the jDOsterior lobe 

 does not increase in size to so marked a degree as the anterior and especially the middle 

 lobe do ; and, conversely, the ultimate subdivision of this lobe is evident at a much 

 earlier phase in the phylogenetic history than that of the other two lobes. 



The most noteworthy featiu-e of the mesial section of the cerebellum in Tars/'/ts is the 

 plumpness aud relative greatness {i. e. iu comparison witli tliat of other small mammals) 

 of the middle lobe of the cerebellum. 



The lowermost part of tliis lobe is much more deeply cut off from the rest than it is 

 in Er'uiacetts and Fei-amclcs. The simple folium so formed represents the " pyramis " 

 of Human Anatomy. It is the dorsal lip of the tissura secunda, and the rest of the 



