66 THE BIOLOGY OF THE FROG chap. 



toes increase successively in length from the first, or inner 

 one, to the fourth, the fifth toe being commonly a little 

 shorter than the third. The first two toes contain three 

 joints each, the third and fifth, four each, and the elongated 

 fourth toe, five joints. On the under side of the articulations 

 between the bones of the toes are small cushions termed 

 subarticular pads. The toes are connected together by web, 

 which serves to make the foot an efficient paddle as the 

 animal swims through the water. The amount of web be- 

 tween the toes varies greatly in different species of frogs, 

 and is a character which is therefore made use of for pur- 

 poses of classification. In Rana pipiens the web extends 

 from the last joint of the first toe to the next to the last 

 articulation of the second toe, then from the last joint oi the 

 second to the next to the last articulation of the third ; from 

 the last joint of the third to a little beyond the second joint 

 of the fourth, and from about the same level on the other 

 side of this toe to the last joint of the fifth. Different indi- 

 viduals vary considerably as regards the extension of the 

 web, especially if they come from different localities, and 

 the above statements, therefore, must not be expected to 

 apply to all cases. 



The ordinary resting position of the frog is a squatting 

 posture, with the anterior part of the body elevated on the 

 fore limbs, which are bent at the elbows and turned inward. 

 Near the middle of the back is a sort of hump due to a 

 bend at this place in the vertebral column. The hind limbs 

 are folded together, the knees pointing outward and forward, 

 and the ends of the ankles lying near each other at the hind 

 end of body. In this position the frog is in readiness to 

 leap, when alarmed, by the sudden extension of the hind 

 legs. 



The skin of the frog is almost everywhere smooth, with 



