(continuation of Order Anura)

Family Ranidae (continued)

• Usually found near water. Some, such as the wood frog spend most of their time in on damp forest floors and often some distance from water. It returns to water only to breed in early spring. Bullfrogs and green frogs are usually found in or near permanent water or swampy regions. The leopard frog R. pipiens found in a wide variety of habitats and with all its subspecies and different forms, is the most widespread of all North American frogs. Commonly used for lab studies. Has been found in nearly every American state and as far north as Canada to as far south as Panama. During winter, hibernates in soft mud of pond and stream bottoms.

Anatomical features of anurans

1. External anatomy:
   1. Integument composition
      1. epidermis
      2. dermis
   2. Coloration of integument due to presence of chromatophores

Chromatophores

pigment cells of the dermis and epidermis; three types:

1. xanthophores - located in uppermost portion of dermis and epidermis; contain yellow, orange, or red pigments
2. iridiophores - located in middle layers of dermis; contain light reflecting (iridescent, "silvery") pigments
3. melanophores - located in lower layers of dermis; contain brown or black colors due to varying amounts of melanin pigment (e.g. the black spots of the leopard frog we have been studying in lab (R. pipiens)

1. Internal anatomy:
   1. Skeletal system:
      1. axial portion of endoskeleton
         1. skull
         2. vertebral column
         3. sternum (breast bone)
      2. appendicular portion of endoskeleton
         1. pectoral and pelvic girdles
         2. forelimbs and hindlimbs
   2. Circulatory system:
      1. Sinus venosus - portion of the systemic circuit which receives deoxygenated blood prior to flow into the heart
      2. Right atrium - chamber of the hear which receives deoxygenated blood due to contraction of the sinus venosus
      3. Left atrium - receives freshly oxygenated blood from the pulmonary circuit. Up to this point, deoxygenated blood and oxygenated blood are kept separated.
      4. Ventricle - receives both oxygenated and deoxygenated blood due to simultaneous contraction of the left and right atria; some partial mixing of the blood occurs, but not as much as would be expected.
      5. Spiral valve - located in ventricle and may act to help keep the blood from mixing.
      6. Conus arteriosus - chamber-like structure that directs the appropriate form of blood (oxygenated or deoxygenated) into systemic and pulmonary circuits, respectively.