A FROG 167 



The Trunk. This body division is short and shows externally 

 no marks of segmentation ; it bears the appendages. In the 

 middle of the back will be noticed a prominent hump, which in- 

 dicates the position of the sacrum, where the hinder appendages 

 articulate with the spinal column. At the posterior end of the 

 trunk and slightly dorsal in position is the small opening of the 

 cloaca, the anus. 



The Appendages. Two pairs of legs are present ; each leg is 

 made up of three divisions, a proximal, a middle, and a distal 

 division. In the foreleg these correspond to the upper arm, the 

 forearm, and the wrist and hand respectively ; in the hind leg, 

 to the thigh, the shank, and the ankle and foot. The toes have 

 no claws. 



The forelegs are relatively short and weak and do not aid in 

 locomotion. Four fingers are present, the thumb being rudi- 

 mentary. In the male frog the first finger is thickened. The 

 fingers are not joined by a web. 



The hind legs are long and muscular and are the principal 

 organs of locomotion both on land and in the water. While the 

 animal is at rest the hind legs are folded together back of it in a 

 position ready for springing. In this position the three divisions 

 of the leg become apparent. In the distal division certain ankle 

 bones are much elongated and make this the longest of the three 

 divisions. The five toes are webbed, the medial (innermost) one 

 being the big toe. 



Exercise 1. Draw the animal as it sits or lies before you. 



If the animal is still alive, it may be killed by placing it in 

 a jar of water in which a small quantity of chloroform or ether 

 has been put. 



Exercise 2, Draw a dorsal view of the extended animal showing the 

 features above mentioned ; carefully label all. 



Exercise 3, Draw a side view of the head. 



The Mouth and Pharynx. Open the mouth as wide as possible ; 

 cut each angle of the jaw a little, if necessary, so that the mouth 

 will remain open. The mouth and pharynx will be seen to be a 



