LoESER, Functions of the Frog s Brain. 367 



be attributed to the excision of the origin or section of the fifth, 

 the sympathetic, or the third nerve, or of all three. This phe- 

 nomenon also proves that these nerves do not appreciably cross. 

 I attribute the upward and outward position of the crossed eye 

 to the fact that its superior oblique muscle is no longer in- 

 nervated, since the nervus trochlearis crosses, and its nucleus, 

 as well as the nuclei of all the nerves that govern the muscles 

 of the eye on the operated side have been excised in the op- 

 eration. Consequently, the superior oblique is the only muscle 

 of the eye on the operated side that is still innervated and this 

 fact explains the downward and upward position of the ho- 

 monymous eye. Since this eye was covered by the nictitating 

 membrane, it is evident that the downward movement of the 

 eye is correlated with upward movements of the nictitating 

 membrane. The persistence of the swallowing and croak reflex 

 after unilateral medullar excision, shows that these are bilater- 

 ally quite independent in the frog and that one side may per- 

 form the function. This operation in conjunction with opera- 

 tion XVII proves that the sense of equilibrium is lost when the 

 origin of the eighth nerve is destroyed. 



The unilateral excision of the medulla anterior to the origin 

 of the vagus group, in conjunction with the unilateral excision 

 of the medulla posterior to the origin of this group, adds the 

 fact that as long as the origin of the vagus grovip is intact, ab- 

 dominal respiratory movements persist on the homonymous 

 side. It is apparently easier to injure abdominal respiration by 

 excisions posterior to the external origin of the vagus group, 

 than anterior to its origin, owing probably to the fact that the 

 deep origin of this group is more posterior than anterior to the 

 external origin. The contracted pupil of the homonymous eye, 

 noted after unilateral excision of the medulla posterior to the 

 origin of the vagus group, was probably due to the destruction 

 of the path of the sympathetic. 



Unilateral excision of the middle third of the medulla in 

 fishes, according to Hyde,^ removes the ganglia for respiratory 



1 Hyde, I. H. American Journal of Physiology, 10, 5, 1904. 



