THE FROG. 33 



In the prepared specimen notice the shape of the body. 

 Can you find scales any where? Is there anything like a 

 tail? How many appendages are there? How do they 

 compare with your own limbs? Open the mouth. Where 

 do you find teeth? Where are the nostrils? Probe them 

 with a bristle. Where does this appear in the mouth? 

 How does the tongue differ from your own? 



Behind and a little below the eye is a circular tympanic 

 membrane (connected with the auditory apparatus). Cut 

 through this and insert a probe. Where does this appear 

 in the mouth? With what does this Eustachian tube most 

 nearly correspond in the shark? See the way the mouth- 

 cavity narrows behind to form the gullet. In front of th : s 

 see the slit-like glottis in the floor of the mouth. 



In the fore limbs do you find parts corresponding to 

 arm, forearm, wrist, palm, and fingers? How many 

 fingers? In the hind leg do you find any parts besides 

 thigh, shank, ankle, instep, and toes? If you have any 

 difficulty, compare the way in which the joints bend with 

 those in your own body, and find where your trouble is. 



INTERNAL STRUCTURE. 



Beginning just in front of the vent, slit the skin forward 

 in the middle line of the ventral surface to a point between 

 the shoulders. Turn back the skin on either side. Is 

 it firmly attached to the underly'ng muscles? Are there 

 blood-vessels on its inner surface? Notice the muscles. 

 Can you find any muscle-plates (myotomes, p. 17 or 25)? 



Next cut the muscles in the same wav, a little to the 



*/ ' 



(animal's) left of the middle line, carrying the incision 

 forward through the hard parts between the shoulders, 

 and taking great care to keep the underlying parts un- 



