Notes upon the Brain of the Alligator. 149 



ventricle, and some of them, at least, pass to the posterior or inner 

 thinned part of the tectum, and thence to the colliculi. The struc- 

 ture of the colliculi is instructive. The whole mass is an intricate 

 complex of cells and fibres. The cells are of two sorts, the smaller 

 being of the flask variety, and constitute the great bulk of the con- 

 tents of the colliculi ; but here and there are large pyramidal cells 

 twice the length of those previously mentioned, (Plate XV., Fig. 9). 

 Although described as pyramids, these cells are rather magnified 

 flask-cells in appearance. As above stated, it seems all but cer- 

 tain that the internal fibre zone of the tectum enters the colliculi ; 

 the fibres uniting with the flask-cells. The fibres from the colliculi 

 seem to descend to the level of the ascending peduncular tracts, 

 and to pass with them to the cerebrum. It is not possible at pres- 

 ent to determine whether the tract from the optic lobes to the 

 corpus posterius issues from the colliculi or from the inner zone of 

 the tectum, without having entered that body. There are some 

 hints of the essential unity of these two bodies, and it may be that 

 they represent but severed portions of an originally simple body. 

 (Plate IX., Figs. 4, 6 and 9.) In the deeper layers of the tract 

 connecting them, is a loose nucleus of large, very irregular cells 

 resembling those of the anterior cornu of the cord, but very elon- 

 gate. (Plate XV., Fig. 8.) The close relation between the optic 

 lobes and the roots of the third and fourth nerves, and a possible 

 connection between the corpus posterius and the roots of the sixth, 

 give us the only clue to the reciprocation between them which we 

 at present possess. 



5. Structure of the cerebellum. The cerebellum is comparatively 

 simple in microscopic structure, and as little attention could be given 

 to it in this connection, it may be dismissed with a reference to 

 the figures (Plate XIII., Fig. n.) The accumulation of so large a 

 number of nutritive and formative cells in its central portion, the 

 great vascularity of the mass, the simplicity of arrangement and 

 single layer of enormous discharging cells peripherally, and the peri- 

 pheral tracts, all seem to favor the current theory that that organ is 

 a storehouse or generator of undifferentiated nervous force at the 

 the disposal of certain distributing centers. One of the smallest 

 and best defined tracts is one passing to it from the optic lobes. 

 The longitudinal sections passing through the peripheral part of the 

 tract of the fourth root, display this fibre bundle, and enable one to 

 trace it into the crura cerebelli. 



