CEREBELLUM OF URODELE AMPHIBIA 3 



the lateral wall of the recess which borders the plexiform evagi- 

 nation is thin but massive. A few flattened neurones are found 

 here, which appear to be greatly reduced Purkinje cells (figs. 17, 

 19). The massive walls of the anterior diverticulum are also rela- 

 tively thin and undifferentiated. 



At the rostral tip of the anterior diverticulum the superficial 

 white layer is very thin and some cerebellar neurones are scattered 

 through it, the stratum griseum thus reaching the external surface 

 of the brain (fig. 22). This is a persistent vestige of a feature 

 which is much more evident in urodele embryos. 



The area acustico-lateralis forms the lateral wall of the fourth 

 ventricle from about the level of the vagus roots fonvard nearly 

 to the tip of the auricular lobe. The taenia ventriculi quarti 

 borders its dorsal surface (figs. 1, 2, 16). It receives the VIII and 

 lateral line VII and X roots and is separated by a distinct longi- 

 tudinal ventricular sulcus from the underlying trigeminal area 

 {s.lat., figs. 1, 3, 16, 27). A short distance caudad of the V roots 

 there is a shallow transverse ventricular sulcus which divides the 

 area into anterior and posterior lobes. The anterior lobe {l.l.l., 

 figs. 1,3, 10, 11, 13, 14, 15, 22) is flatter than the posterior lobe and 

 does not extend forward quite to the rostral tip of the auricular 

 lobe. 



The area acustico-lateralis corresponds to the structure which 

 students of fish brains have commonly called the tuberculum acus- 

 ticum (including the lobus lineae lateralis) ; but this stmcture in 

 both fishes and amphibians is more nearl}^ comparable with the 

 entire area acustica of manmials than with the tuberculum acusti- 

 cum. The latter term, accordingly, should no longer be applied 

 to brains of the Ichthyopsida. Norris, in his descriptions of Am- 

 phiuma ('08, p. 536) and Siren ('13, p. 283), has identified an 

 area of neuropil which forms the most dorsal part of the stratum 

 album in the region of the VII and VIII nerves with the lobus 

 lineae lateralis of fishes. This area receives the most dorsal lat- 

 eral line root of the facialis and was referred to by Kingsbury 

 ('95, p. 187) as the dorsal island of alba. 



The recessus lateralis is bounded rostrally by an obliquel}^ 

 transverse lamina of nerv^ous material which we shall later recog- 



