1 8 THE FROG 



5. The anus (posterior opening of the digestive tube). 

 It is slightly dorsal in position. 



6. The anterior nares, or external openings of the nasal 

 cavities. 



7. The fore limbs. There are three divisions, upper- 

 arm, fore-arm and hand (manus). The wrist, forming 

 the proximal portion of the manus, is scarcely distinguish- 

 able externally. In the male there is a thickening along the 

 inner edge of the first finger, which is especially prominent 

 during the breeding season. 



8. The hind limbs. There are three divisions, thigh, leg 

 and foot (pes). Certain bones of the proximal part of the 

 foot (the ankle) are greatly elongated; of what advantage 

 is this to the frog? What is the function of the web of the 

 hind foot? 



III. THE MOUTH CAVITY. 



For the following study both recently killed and pre- 

 served specimens are desirable. 



A. Open the mouth of a frog to its fullest extent and ob- 

 serve : 



i. On the roof: (a) The teeth. 



(1) Maxillary teeth on the edge of the upper jaw. 



(2) Vomerine teeth, two groups on the fore part of the 

 roof. Count them with the aid of a dissecting needle; about 

 how many teeth in each group ? Is the number constant in 

 different frogs? 



(3) Using a dry prepared skull, examine a maxillary 

 tooth carefully with a hand lens. Distinguish crown and 

 root. How are the teeth inserted on the jaw bone (i. e. } in 

 sockets or otherwise) ? Do they offer more resistance to an 



