MOEPIIOLOGY OF THE BliAIX IX THE jr.\M.M.\LIA. 431 



from tbose of the area C. The connection of the copula pyrainidis with tlie pyrainiil 

 becomes either entirely destroyed or reduced to exceedingly insignificant proportions. 

 From comparative studies of the udult cerebellum it is quite imiiossible to decide the 

 fate of the copula pyramidis in the larger cerebella. In many brains it seems to dwindle 

 or completely disajipear. In others again, especially Siiiiia salynts, it seems to undergo 

 enormous expansion and form the greater ])art, if not the whole, of tiie body which 

 is called tonsilla (amygdala) in Human Anatomy. This is a problem which can only ])e 

 certainly settled, by a study of its developmental history in a series of mammals. 



The relations of these parts are considerably disturbed in the genera S/iiiic, JiUhrop<i- 

 jnilu'cus, and Homo by the extreme dwindling of the paraflocculus and the consequent 

 disappearance of its •' petrosal " part. The parafloccular remains become the flocculi 

 secuudarii of ITenle, 



Of the various subdivisions of the middle lobe of the cerebellum in Lemur, the area A 

 is subject to perhaps the least change. It becomes furrowed by numerous new fissures, 

 but they are approximately parallel to the fissura prima, and hence do not greatly 

 disturb the pattt-rn. The area A represents the lobus lunatus posterior, and is mesially 

 continuous Avith the region between the fissura prima and the fissura b, which is called 

 the clivus monticuli in Human Anatomy (tig. 05). 



The area B is a very jdump rounded mass "ivhieli forms the lateral pole of the 

 cerebellum (fig. 65). It consists of twelve vertical folia radiating in a feather-like pattern 

 from a very narrow vertically-placed leaf-like stalk, the mesial part of which is deeply 

 buried between the areas A and C. This stalk does not reach the nu;!sial plane, for 

 it becomes fused to the posterior aspect of the area A. The area B is the lobus postero- 

 superior. There is no separate folium cacuminis. 



The area C is a plump vertical worm-like band wedged in between the area B and the 

 mesial parts of the middle and jiosterior lobes on the caudal surface of tlu; cerebellum. 

 Its connection with the suprapyraniidal part of the " Aermis " is constricted and depressed 

 in a vertical furrow. In the Apes tliis vertical band rapidly increases in breadth, and 

 the direction of its folia becomes oblique. 



The general features of the anterior lobe are remarkably constant in all Mammals. 

 The differences consist chiefly of an increase in the number of lissurcs in proportion 

 to the size of the cerebellum. 



In all other Prosimi:e tlie structure of the cerebellum does not vary to any marked 

 extent from that of lAtiiur. In the smaller members the fissures become much fewer, 

 and in Mieror-ebus we find an orgt,n which differs very slightly from that of Tarsins. In 

 Chiromys tbe primitive connection between the pyiamid and tlie parallocculus, wiiicii 

 has been seen to become obscured in Lemur, is retained in a distinct form. 



[Since the foregoing pages were in type, seme supplementary notes Iiave been received from tlie 

 author. In order not to delay the issue of this part, it is intended to publish the notes mentioned in an 

 early number of the ' Journal ' (Zoology), vol. 28.— Sec. Lin.n. Soc] 



SECOND SEKIES. — ZOOLOGY, VOL. VIII. (j^ 



