XX Journal of Comparative Neurology. 



which in horizontal sections is seen to be due to the entrance of fibres 

 from without. 



The medulla is very simple and is wedge-shaped with the broad- 

 est portion at the entrance of the trigeminus. The form is wonder- 

 fully like that of the human at an early stage. The hypoglossus 

 emerges in two bundles from the ventrolateral aspects. 



The vagus consists of a motor portion with three ventral roots 

 which arise in niduli, corresponding to the ventral cornua, and four 

 chief groups of fibres on the lateral aspects : i, a small root lying 

 dorsad of the caudal motor root and receiving the fasciculus solitarius; 

 2, in front of this a bundle with three lateral fibres from lateral niduli 

 and two apparently sensory bundles ; 3, a group with four lateral 

 bundles at the same time containing ascending fibres ; 4, a cephalic 

 group of two roots, one bemg sensory, the other lateral motor. 



The glossopharyngeal emerges somewhat cephalad with two 

 closely associated sensory and one motor root containing fibres from 

 its nidulus and the fasciculus communis. 



The acustico-facial is the largest nerve which emerges from the 

 medulla. A dorsal root (VII) emerges from an adjacent motor nidu- 

 lus and also contains sensory fibres passing to the dorsal region of the 

 medulla. Ventrad of this is a large root from the fasciculus com- 

 munis also containing sensory fibres (VIII, i). The strongest branch 

 lies just ventrad of the above and is the same plane as the cells which 

 give rise to Mauthner's fibres (VIII, 2). The remaining roots lie 

 still ventrad. 



Burckhardt discovered fibres corresponding to the sixth and 

 fourth, thus showing that Weidersheim's statement that the Dipnoi 

 lack the abducens and trochlearis was founded on insufficient infor- 

 mation and completing the evidence that these nerves are common to 

 all vertebrates. 



The trigeminus contains fibres from its nidulus in the floor of the 

 metencoel and mescencephalic nidulus, which latter is connected by 

 fibres passing through the cerebellum. The sensory contingent is 

 composed of the ascending root and cerebellar fibres. 



The cerebellum resembles that of amphibia. Cells are found in 

 its basal and lateral portions, but Purkinje cells are absent. 



The fibres contained are (i) decussating tracts from the mesen- 

 cephalic nidulus of the trigeminus ; (2) fibres passing from the latter 

 cells to the acusticus; (3) fibres which decussate and pass cephalad of 

 the opticus (?). This tract compares with the cephalic cerebellar pe- 



I 



