6 - FROG MAJOR EXTERNAL ORGANS

• What modification in the frog’s body is associated with its locomotion?

  Body modifications
• Which limbs are enlarged to support jumping and swimming?

  Hind limbs
• Which limbs are relatively small compared to the hind limbs?

  Forelimbs
• What forms the compact central mass of the frog’s body?

  Rest of the body
• What part of the body is reduced, limiting head movement?

  Neck
• What structural change in the vertebral column limits the central body mass's freedom?

  Shortening and fusion of vertebral elements
• How is the frog’s head shaped dorsoventrally?

  Flattened
• What is the advantage of the frog’s head being rounded?

  Reduces resistance in water
• What two types of eyelids are present in the frog’s eye?

  Upper and lower eyelids
• What additional membrane protects the frog's eye underwater?

  Nictitating membrane
• What is the color and texture of the nictitating membrane in preserved specimens?

  White fold of skin
• Where is the nictitating membrane located in relation to the eyelids?

  Beneath the eyelids
• What does the nictitating membrane allow the frog to do underwater?

  Protect eyes while still seeing
• How can you expose the nictitating membrane during examination?

  Pull lower eyelid forward and lift
• What is the term for the frog’s eardrum?

  Tympanum
• Where is the tympanum located relative to the eye?

  Posteroventral to the eye
• How does the tympanum compare in size to the eye?

  Slightly larger
• What openings serve as nostrils to the outside?

  External nares
• What adaptations make the hind limbs efficient for locomotion?

  Large and muscular
• What swimming stroke performed by humans is similar to the frog’s swimming movement?

  Frog kick
• What structure between the toes of the hind feet aids in swimming?

  Webbing
• How does webbing between the toes increase swimming efficiency?

  Provides resistance in water
• What is the scientific term for the frog’s hand?

  Manus
• What is the scientific term for the frog’s hind foot?

  Pes
• Which digit of the manus is greatly reduced?

  Thumb (pollex)
• What is the special function of the thumb (pollex) in male frogs?

  Nuptial pad for grasping female
• Where is the anus located in relation to the hind limbs?

  Between the hind limbs
• What is the positional orientation of the anus on the body?

  Dorsal
• The anus serves as the opening to which common terminal cavity?

  Cloaca
• What three systems share the cloaca as their common terminal portion?

  Digestive, excretory, reproductive
• What large vein in the thigh is cut open during preparation?

  Sciatic vein
• What material is injected into the posterior veins through the sciatic vein?

  Blue latex
• On which side of the body is a transverse incision made to expose the heart?

  Ventral side
• The incision to expose the heart is located just posterior to which limbs?

  Forelimbs
• Which chamber of the heart is used to inject red latex into the arteries?

  Ventricle
• What is the purpose of injecting red latex into the arteries?

  To highlight arteries
• After arteries are injected, what other vessels are injected to complete the process?

  Veins
• Why are latex injections especially helpful in anatomical dissection?

  Differentiate arteries and veins
• What important function does the frog’s skin serve aside from protection?

  Respiration
• Why must the frog’s skin always remain moist in life?

  It lacks scales to prevent water loss