CLASS AMPHIBIA 



503 



lobes have an inhibiting influence on the reflex activity of the 

 spinal cord. The cerebellum apparently has no important func- 

 tion in the frog. Many activ- 



ities are still possible when 

 everything but the medulla 

 is removed. The animal 

 breathes normally, snaps at 

 and swallows food, leaps and 

 swims regularly, and is able 

 to right itself when thrown 

 on its back. Extirpation of 

 the posterior region of the 

 medulla results in the early 

 death of the frog. The brain 

 as a whole controls the actions 

 effected by the nerve-centers 

 of the spinal cord. " The 

 higher centers of the brain 

 are comparable to the cap- 

 tain of a steamer who issues 

 orders to the man running 

 the engine when to start and 

 when to stop, and who has 

 his hand on the wheel so as 



to guide the course of the 

 vessel." (Holmes.) Cranial 

 nerves I to X (see p. 409, 

 Table XIV) are present in 

 the frog. 



The Spinal Cord (Fig. 

 423). — The spinal cord ex- 

 tends backward from the 

 medulla and ends in the uro- 

 style. It' is surrounded by 

 two membranes, an outer 



Fig. 423. — Nervous system of the 

 frog. Br, brachial nerve ; Js, ischial 

 nerve ; 0, eye ; 01, olfactory nerve ; 

 Op, optic nerve; Spm, ist spinal 

 nerve; Sgi-io, ten ganglia of sympa- 

 thetic system; Vg, gasserian ganglion: 

 Xg, ganglion of vagus. (From Sedg- 

 wick's Zoology, after Ecker.) 



