Frog Dissection Notes

Introduction to Frog Dissection

• Focus on external anatomy and adaptations for life in water and on land.

External Anatomy of the Frog

• Skin:
  • Thin, akin to saran wrap for easy gas exchange; mainly breathes through skin.
• Back Legs:
  • Webbed feet designed for swimming.
• Eyes:
  • Protected by a nictitating membrane that flips up underwater to shield from abrasions.
• Tympanum:
  • The ear structure of the frog.
• Cloaca:
  • Common opening for excretory and reproductive systems (digestion, urine, sperm/eggs).
• Leg Muscles:
  • Large muscles for jumping; strong spine to support jumping.
• Coloration:
  • Dark dorsum and light ventral side (countershading) for camouflage against predators.

Internal Anatomy - Mouth Structures

• Opening Mouth:
  • Make small cuts in mouth corners to ease opening.
• Tongue:
  • Attached at the front, flips out to catch prey.
• Teeth:
  • Vomerine Teeth: Two prominent teeth for holding prey.
  • Maxillary Teeth: Ridges around gums for grip, not for chewing.
• Nostrils:
  • Known as internal nares.
• Eustachian Tube:
  • Equalizes pressure and connects to the eardrum.
• Glottis:
  • Opening to the lungs.
• Esophagus:
  • Opening posterior to the glottis.

Dissection Procedure

1. Cutting Skin:
   • Cut from groin to mouth, only through skin initially.
2. Observing Blood Vessels:
   • Vascular skin aids gas exchange.
3. Cutting Musculature:
   • Careful incision to avoid organs, then reflect muscles back.
4. Identifying Organs:
   • Oviducts: Female reproductive structures; large number of eggs visible.
   • Liver: Large lobes, produces bile for digestion.
   • Stomach: Muscular for digestion (not chewing).
   • Intestines: Small and large; named for diameter, not length.
   • Mesentery: Supports organs and houses blood vessels.
   • Spleen: Small, purplish organ near liver.
   • Kidneys: Bean-shaped organs that filter nitrogenous waste.
   • Urinary Bladder: Stores urine, exits through cloaca.

Heart and Lungs

• Heart:
  • Three-chambered heart (two atria, one ventricle).
• Lungs:
  • Small compared to skin surface area; mainly rely on skin for respiration.

Observations

• Stomach Contents:
  • May contain undigested food; folds allow for expansion.
• Small Intestine:
  • Folds increase surface area for digestion and absorption.
• Comparative Structures:
  • Frog lungs are hollow, unlike the solid structure of mammalian lungs with alveoli.

Conclusion of Dissection

• Review structures (heart, lungs, kidneys, intestines) and their functions in the frog's anatomy.