CLASS AMPHIBIA 499 



the head to the other and has an upper and lower jaw. The anus 

 or vent is at the extreme posterior end of the trunk. 



The forelimbs are composed of the upper arm, which joins the 

 trunk, the forearm, wrist or carpus, and the hand with its four digits. 

 In the male, particularly during the breeding season, the innermost 

 digit, or thumb, is enlarged, whereas the thumbs of females remain 

 apparently the same size. The digits may have tubercles on them, 

 and their positions in relation to various bones of the hand give rise 

 to specific names for these tubercles. The forelimbs are used not 

 only to help support the body but also as an aid in pushing food 

 into the mouth. 



The hindlimbs are long and have powerful muscles. Bullfrogs 

 ordinarily leap about three feet but can easily cover a distance of 

 five or six feet. The hindlegs are composed of the thigh, which 

 joins the trunk ; the shank; and the ankle, or tarsus. Following the 

 tarsus is the foot with five digits (toes), which are connected by a 

 web, producing a very efficient swimming organ. 



The smooth damp skin, which is soft and loosely attached to the 

 body except in the head region, is composed of two layers, an outer 

 epidermis and an inner dermis. The skin is pigmented and very 

 rich in mucous glands, which aid in keeping it moist. Bullfrogs 

 moult or shed the superficial layer of epidermal cells of their skin 

 at varying intervals. 



Dig^estive System and Digestion 



The mouth cavity, or buccal cavity continues directly into the phar- 

 ynx with no sharp line of bounjiary between them. The latter narrows 

 toward the esophagus, which is a short gullet leading directly from the 

 pharynx to the stomach. The lining of the esophagus has a number 

 of longitudinal folds and is ciliated. The stomach normally lies on 

 the left side of the body. It is curved, with the convex side toward 

 the bullfrog's left. Its anterior or cardiac end is wide, and the 

 pyloric or posterior end is narrowed and constricted where it joins 

 the small intestine. The duodenum, or anterior part of the small 

 intestine, runs forward almost parallel with the stomach. At the 

 point where the intestine turns back posteriorly the duodenum be- 

 comes the ileum, which composes the remainder of the small intestine 

 and is considerably coiled. The large intestine or rectum is sharply 



