Her RICK, Morphology of Brain of Bony Fishes. 59 



drawback in homologizing these structures by recognizing the 

 mammillaria in their normal position immediately caudad of the 

 infundibulum, leaving us free to interpret the hypoaria in ac- 

 cordance with their position and contained structures. In other 

 vertebrates the region between the tuber and the pons is occu- 

 pied ventrally by the pes pedunculi or crusta. We have fortu- 

 nately a very definite landmark in the decussation of the middle 

 peduncles of the cerebellum, which is exceedingly distinct lying 

 at and just caudad of the exit of the oculomotor nerve. In this 

 region the greater number of the ventral peduncular bundles 

 end. Says Ranney, "Some of the efferent fibres of the cere- 

 brum probably leave the direct tract of the projection system 

 within the region of the pons, passing to the cerebellum." 

 "Cross sections of the region of the pons reveal the fact that the 

 transverse fibres of the processus cerebelli ad pontem may be 

 divided into three sets, as follows: i, a superficial layer; 2, 

 fibres which interlace with longitudinal fibres escaping from the 

 cms; 3, a deep seated layer. The superficial and deep-seated 

 layers appear to be perfectly independent of any association 

 with the fibres belonging to the middle projection system of the 

 cerebrum (those of the crusta and tegmentum cruris.) Meynert, 

 however, brings forward certain reasons, based upon a minute 

 study of the general relations of these layers, which apparently 

 lend support to the view that the fibres of these strata are in 

 communication with nerve cells imbedded in the pons, and that 

 certain fibres are likewise joined to these cells, and that the two 

 sets of fibres are thus brought into communication with each 

 other." This assumption we are fortunately able to demonstrate 

 in the most satisfactory way. The fact that the ventral pedun- 

 cular bundle, whose fibres have been traced to the cells of the 

 fore part of the hemispheres, find their apparent termini in the 

 posterior portion of the hypoaria, is sufficient to point to the 

 latter as expansions of the pes pedunculi or, specifically, the 

 crusta. In all animals higher than fishes there is a layer of 

 densely staining matter separating the crusta from the tegmen- 

 tum, the substantia nigra. In all cases where we have examined 

 it this region has a nidulus of very peculiar cells, whose numer 

 ons branches include at least two axis-cylinders and apparently 

 more. This the author has called in the reptilia, nidulus niger. 



