MEDULLA OBLONGATA CEREBELLUM. 1 6 



sertion, and in the absence of direct proof to the contrary, it would be 

 unwise to claim that the division, above given, of the centre for the acous- 

 tic nerve, is correct, in spite of equally positive assertion, and appearan- 

 ces, some of which, especially in reptiles, are favorable to the more mod- 

 ern view and opposed to that of Deiters. 



In the frog, cross sections of the pars commissuralis, including the 

 cerebellum, contain a group of cells, (shown in Plate LVIII.) which 

 are seen to be in close relation to some of the lower fibres of the trigem- 

 inus. This bundle of fibres may justly be regarded as the motor portion 

 of the trigeminus, from its evident relation to cells having about the 

 same position as the motor-trigeminal cells of reptiles. In saurians, 

 chelonians and ophidians, this centre of origin is more easy of demon- 

 stration than in the frog. 



Plate L. gives a good representation of the position of this ganglion 

 in the alligator, and its relation to the fibres of the motor-trigeminal root ; 

 the latter extending obliquely downwards from the cells towards the 

 border of the white substance. In Plate CII. the same group is enlarged 

 300 diameters. Plate LVI. iv shows the same parts in the turtle. 



THE CEREBELLUM. 



PLATES LXIII. LXIX. all from longitudinal vertical sections, facili- 

 tate a comparison of the different shapes of the cerebellum and its posi- 

 tions in relation to the optic lobes, in reptiles and batrachians. 



Beginning with the alligator, Plate LXIII. the vertical por- 

 tion on the right of the photograph, is next the optic lobes the 



organ is seen to be folded backwards upon itself, increasing its volume 



