THE CEEEBELLUM. 



573 



Pons--l- 



Fl, 



Olivet 



ss. pnma 



--Ffss. postlunarfs 



r . ere is no justification for such a subdivision, nor is any useful purpose served by linking 

 t ether two parts so distinct, morphologically and physiologically, as the culmen and declive 

 si giving the name monticulus to the complex. 



Only some of the fissures of the vermis become prolonged laterally beyond the 

 1 lits of the vermis, but as the boss-like lateral lobes begin to expand, their surface 

 1 iomes folded and a series of independent lateral fissures are formed. [The anterior 

 I e, however, is prolonged laterally upon each side into tapering wings and all the 

 jmres in them are merely prolongations of the fissures of the vermis.] 



After the limiting fissures of the flocculus and paraflocculus, the first independent 

 f sure to make its appearance is one which develops behind and almost parallel to 

 t '. lateral prolonga- 

 tns of the fissura 

 jma. Kolliker called 

 t; intervening strip of 

 c;ebellum lolulus 

 I latus posterior and 

 t fissure may be called 

 fim'ra postlunaris. 

 lese postlunar fissures 

 fy;in far out on the 

 Ii3ral swelling in the 

 f( rth monthandgradu- 

 a, 7 approach the median 

 pne, where they may 

 nst and become con- 

 flmt on the vermis. 

 It it often happens 

 tt they do not meet, 

 ii vvhich case no folium 

 vtnis is cut off the 

 d live. 



At the end of the 

 ft rth or beginning of ^^r^iffli^^^^^^^ 3 k develo f7 



fissure horrzontdis 



line of floor of 

 fissura horiiontalis 



is*, p r i m a 



|L--fiss. postlunaris 



floe.- 



Fiss. para pyramid ali s 



FIG. 



B 



08. THE LEFT LATERAL ASPECT OF THE F(ETAL RHOMBENCEPHALON 

 AT THE FOURTH (A) AND FIFTH (B) MONTHS. 



The cerebellum is stippled. 



tl fifth month an oval 

 selling makes its ap- 

 p ranee upon each side 

 o:bhe uvula upon the 

 iiTior surface of each 

 laxal lobe (Fig. 505). 

 T s is called the tonsilla 

 c< belli or tonsil, and 

 t fissure which de- 

 vops behind it and 

 d< mits it is called post- 

 tc lillar. Asa rule the 

 ^ post-tonsillar fissures become confluent with the fissura secunda upon the vermis 

 the whole furrow in the adult may be called fissura secunda. At the middle of the 

 fiJ i month a lateral fissure, called parapyramidal, makes its appearance some distance 

 bt ind the post-tonsillar, from which it is separated by an area called the lobulus 

 bi nter. As a rule, these parapyramidal fissures become confluent with the supra- 

 Pi imidal fissure. The whole furrow is known in the adult by the latter name, 

 issure to which most importance is usually attached develops quite late in the 

 hi lan cerebellum, and not at all in that of the great majority of other animals. It 

 lied the fissura horizontalis cerebelli. In the adult it begins upon the front, where 

 i brachium pontis plunges into the cerebellum, and the furrow is formed in a 

 ^3 or less mechanical way by the bulging forwards (above and below the cerebellar 

 e mcles) of the exuberant mass of the cerebellar hemispheres. The actual infold- 

 is preceded by the appearance of several irregular depressions (Fig. 508) in the 

 e where the horizontal fissure will develop. This fissure begins in front and 



