406 REFLEX ACTIONS. 



CHAPTER XXXIII. 

 REFLEX ACTIONS. 



REFLEX actions are best studied in the frog, the brain hav- 

 ing first been removed, or at least separated from the spinal 

 cord. The strongest and healthiest frogs should be chosen for 

 the purpose. The student should make himself acquainted 

 with the general form of the dried frog's skull. This having 

 been done, the position of the occipito-atlantal articulation 

 may readily be recognized on the living animal. 



nsion nftln; Medulla Oblongata. Having wrapped a cloth 

 round the hind legs and body of the animal, clasp the fore legs 

 round the ring finger of the left hand, and hold them in posi- 

 tion by the middle and little fingers, which should also hold 

 tight the cloth. Press down the tip of the frog's nose with the 

 thumb of the same hand, so as to bend the neck as much as 

 possible. If the fore-finger of the right hand be now made to 

 glide over the roof of the skull, exactly in the mid-line from 

 before backwards, a slight but distinct depression will be felt 

 in the neck at the point where the occiput ends, and where the 

 medulla is covered, not by bone, but by the occipito-atlantal 

 iiu-iiibrane. It lies in a line drawn across the skull at a tan- 

 gent to the hinder borders of the two membrana tympani. (Fig. 

 2GG, line a-/>.) 



The position of this point being satisfactorily ascertained, 

 with a sharp-pointed scalpel make a small transverse incision 

 across it about a few millimetres long. The incision should 

 not be ran ifd too far on either side. If the blood, which comes 

 freely, be rapidly taken up with a sponge, and the neck be kept 

 well bout, the medulla will be clearly seen. This should now 

 be completely cut across, and the wound be rapidly sponged, 

 in order that the division may be ascertained by aetual inspec- 

 tion to be complete. The encephalon may then be completely 

 destroyed by introducing a blunt piece of wire into the wound, 

 and evi^eeratinu; the skull. If the wound be then left to itself 

 the bleeding will, in most cases, soon cease ; if not. a small plug 

 of woo<l (the sharpened end of a lueifer match) ma}' be thrust 

 into tl'c skull. This, however, should be avoided if possible. 

 It is better to conduct the operation in this way, seeing clearly 

 what is being done, than to divide skin, membrane, and medulla 

 by one thrust, without being able to tell exactly whether the 

 division is complete. 



