6o Journal of Comparative Neurology. 



In mammals the nidulus is less compact and such cells are scat- 

 tered widely in the region. In the corresponding region of 

 fishes, dorsad of the ventral peduncular tract and separating it 

 from the tegmentum with the dorsal peduncular fibres, is a very 

 strongly developed nidulus forming the medullary ])art of the 

 hypoaria and the transition between the three sets of 

 fibres; viz., the ventral and dorsal peduncles and the tract to 

 cerebellum. The origin of the fibres can be seen with all de- 

 sirable distinctness. A comparison of such a figure as Fig. 72, 

 in Edinger's Lectures on the Nervous System, with a section 

 through the posterior part of the hypoaria of fishes, reveals com- 

 plete similarity. The apparent differences grow out of the short- 

 ening of the axis by which the enormously developed optic tec- 

 tum is crowded backward, the cerebellum forward and the 

 aqueduct is expanded in such a way as to puff out the sides of 

 the crusta. The nigra and nidulus ruber sustain normal rela- 

 tions and fibre connections. The position and character o( the 

 niduli of the tegmentum are especially helpful in determining 

 homologies in this region. 



The most characteristic of these cell masses has m all 

 groups of animals a peculiar suffused color which has earned for 

 it the term red nidulus (nucleus ruber.) In man this is composed 

 of granular masses and nerve cells. The processus e cerebello 

 ad testes or superior peduncle of the cerebellum comes into close 

 relation with it and the region is filled with large multipolar cells 

 which are closely associated with very numerous blood-vessels. 

 Meynert describes the branches of the cells as running in the 

 walls of the vessels. Such a peculiar structure is not easily mis- 

 taken if present and what we have to add respecting the nucleus 

 rotundus of fishes will serve to establish the homology. 



The nidulus ruber m mammals occupies a conspicuous place 

 in the tegmentum and is mesad and caudad of the corpus sub- 

 thalamicum or body of Luys. The fibres of the tegmental radi- 

 ation "lie outside of and above the red nidulus, surrounding 

 about a third of that ganglion like a capsule," (Edinger, p. 94). 

 Passing caudad they form a tract of fibres which is variously 

 known as lemniscus, laqueus. or fillet (schleife). Fibres from 

 the thalamus enter the nidulus ruber. Professor Fritsch de- 

 scribes the body, which we unhesitatingly regard as the homo- 



