208 THE BIOLOGY OF THE ANIMAL 



the thumb and fingers. Where do you feel the 

 hard parts of the skeleton ? Note the " hump " 

 in the back of a living frog which is sitting 

 naturally. JSTote also the ridge, the urostyle, 

 running backward from the " hump," and end- 

 ing near the posterior end of the trunk. Find 

 at the posterior end the cloacal aperture. 

 What is its exact position ? Shape ? What is 

 its position with regard to the end of the uro- 

 style? 

 3. The limbs. — Study first the anterior limbs. To 

 what part of the body are they attached ? In 

 which direction do they project ? What is their 

 shape 1 Are they long enough to reach to the 

 tip of the head? What is their diameter ? Does 

 it vary greatly at any point? Make out the 

 following regions on each limb : the brachium 

 or upper arm, the antebrachium or fore arm, 

 and the manus or hand. What portion of the 

 entire limb does each of these regions form ? 

 In which direction does each point? Compare 

 the brachium and antebrachium with regard to 

 length. How many digits or fingers on the 

 manus ? Is the pollex or thumb present ? Of 

 how many joints does each digit consist ? Do 

 you find a web between the adjacent digits ? 

 Do they difi'er at all with regard to the thick- 

 ness of the skin covering them ? Do they bear 

 nails or claws ? 



Study the hind limb, and make out the fol- 

 lowing regions : the femur or thigh, the crus 

 or leg, and the pes or foot. Compare as above 

 all of the regions with one another and with 

 the corresponding regions of the fore limb. 



