364 Journal of Comparative Neurology and Psychology. 



optic nerve is not in the optic lobes. The fact that the sHght 

 defect in sight disappeared two weeks after the operation, indi- 

 cates that its cause was inhibitory stimuH. By excising 

 the lobi and thalami optici unilaterally it was proved that the 

 nervus opticus of the frog crosses completely at the chiasma. 

 The abnormal retention of urine and the straight forced move- 

 ments — always noted after excising the anterior and posterior 

 half of the lobi optici respectively seemed to be caused by ab- 

 normal stimuli due to direct loss of association fibers. It indi- 

 cates that the anterior part of the lobi optici is in close connec- 

 tion with the sacral urinary ganglia and the posterior, with some 

 important motor nucleus. 



My observations and conclusions regarding the optic nerve 

 agree with those of Singer and Munzer\ Wiedersheim- . and 

 ScHRADER, who found that in fishes, reptiles and amphibia the 

 decussation of the second nerve seems to be complete, and that 

 the centres of the nervi optici are located in the thalami optici. 

 My results agree neither with those of Donaldson^, who states 

 that the frog loses the power to avoid obstacles when the optic 

 lobes are removed nor with those of Landois^ who says that 

 destruction of the optic lobes in birds, amphibia and fish is fol- 

 lowed by blindness. 



The unsteady and weak jumps, flat position of the body 

 and the tendency to abnormal hibernation, following bilaterial 

 cerebellar excision, I believe to be due to the weakened condi- 

 tion of the limbs, to a loss of muscular tone, as well as to a loss 

 of timely sequence or co-ordination and gradation according to 

 the strength of the contractions, i. e., sensory ataxia. It seems 

 that these deficiency phenomena are to be explained by the ab- 

 sence and modification of normal impulses proceeding from or 

 going to the cerebellum. Anatomically, the explanation might 



1 Singer and Muzner. Detikschriften der mathematik-natunvissenschaftlicheH 

 Classe der Kaiserlichen Akademie der IVissenschaften, 55, 1888. 



* Wiedersheim. Vergleichende Anatomic der Wirbelthiere, and Edition, 

 335, 1886. 



' Donaldson, H. H. American Textbook of Physiology, 708, 1897. 



* Landois, L. Textbook on Human Physiology, 805, Ig04. 



