CEREBELLUM OF URODELE AMPHIBIA 15 



CRYPTOBRANCHUS 



In Cryptobranchus alleghaniensis the cerebellum is arranged 

 essentially as in Necturus, but the organ as a whole is better devel- 

 oped. The recessus posterior mesencephali is very e\ddent, 

 while the recessus laterahs rhombencephali is less extensive than 

 in Necturus. The latter does not extend forward as an anterior 

 diverticulum beyond the transverse level of the decussatio veli 

 and its roof is wholly membranous. The body of the cerebellum 

 is more massive than in Necturus and a thin column of cells, in 

 addition to the epend\Tna, connects the stratum griseum of the 

 two sides across the roof in connection with the commissura cere- 

 belli. The anterior lobe of the area acustico-lateralis is separated 

 dorsally from the posterior lobe by a deep sulcus. It extends 

 forward to the lateral angle of the recessus lateralis, where it 

 fuses broadly with the body of the cerebellum. The fiber tracts 

 have not been studied in detail, but so far as observed, they con- 

 form to the description already given for Necturus. 



The cerebellum of Cryptobranchus occupies an intermediate 

 position between those of Amphiuma and Amblystoma. 



SUMMARY 



The cerebellum of mammals is known to develop from the 

 rhomboidal lip bordering the lateral recesses of the fourth ventri- 

 cle. The early embryonic stages of the human cerebellum re- 

 semble rather closely the adult condition of Necturus save for 

 the absence in the latter case of the pons flexure. 



In Necturus each lateral recess is continued forward into a 

 blind anterior diverticulum whose walls are massive on all sides. 

 Cerebellar tissue is present in the antero-medal wall and the 

 floor of the lateral recess and in the walls of its anterior diverticu- 

 lum in the auricular lobe. The postero-lateral wall of the lateral 

 recess is formed by a thickening, the anterior lobe of the area acus- 

 tico-lateralis, intermediate in structure between the cerebellum 

 and the posterior or primary lobe of the area acustico-lateralis. 



The thin plate of cerebellar tissue in the antero-medial wall of 

 the lateral recess of each side is called the body of the cerebellum 



