Download Class Amphibia: Organisms with 2 lives (in

Bio 200-Lab Lecture 6
Frog Dissection
Class Amphibia: Organisms with 2 lives (in water and on land)
I- External features:
- Bilateral symmetry
- Directional terms: -Dorsal surface
- Ventral surface
- Anterior
- Posterior
- Lateral
- Medial
- Frog’s body: Head + Trunk + Pectoral girdle + Pelvic Girdle
- Skin: kept moist by many mucous glands to minimize water
loss; may also have poison glands
Highly vascularized; Primary organ of gas exchange
- Head: - Eyes with nictitating membrane (Transparent
eyelid)
- Tympanum : Circular membranous area found
posterior and lateral to the eyes
- External nares (nostrils): small pitlike openings on
the anterior of the head, connected to the oral cavity
through internal nares.
- Limbs: Fore limbs: 4 digits
Hind limbs: 5 digits
Webbing between the toes
II- Internal Features:
1- Oral Cavity:
Cut the corners of the mouth to open it all the way and observe:
- Internal nares
- Large opening into esophagus + small glottis
- Eustachian tubes (connect to the middle ear)
- In males: vocal sac apertures
- Vomerine teeth
- Maxillary teeth: row of teeth on upper jaw
- Tongue is hinged anteriorly
2- Respiratory Tract:
Tadpoles: gills for respiration
Adults: Skin
Mucous membrane of the mouth
Lungs
Lungs: thin sacs protruding from below the liver on either side
of the heart
3- Digestive Tract:
- Esophagus
- Stomach : Huge, J-shaped, at the left side of the body
In frogs, digestion starts in the stomach
- Small intestine: Separated from stomach by pyloric
sphincter . Digestion is completed here.
- Large intestine: Water resorption and feces formation:
Undigested food is stored in large intestine
until the animal defecates
It ends as a rectum
- The liver: Large, 3-lobed
Produces bile which aids in the digestion of fats
Stores and interconverts carbohydrates, fats and
proteins
Destroys toxins; Helps in blood coagulation
- Gallbladder: Bluish green; stores bile before it is released into
the small intestine
- Spleen: Deep red round organ found near the small intestine.
Not a digestive structure. It cleans the blood:
destroys old RBC. It helps in the production of new
blood cells and of antibodies.
3- The Urogenital System:
-Kidneys: Flat and reddish, about 1 inch long, in the dorsal part
of the abdominal cavity.
Remove wastes from blood and form concentrated
urine.
- Adrenal Glands: Yellow stripe on the ventral surface of each
Kidney
= endocrine glands that produce epinephrine.
- Testes: 2 white bean-shaped structures at the anterior ends of
the kidneys
- Ovaries: Near the anterior end of the kidneys, may be filled
with eggs
- Oviducts: White coiled thread-like tubes.
Small and nonfunctional in males.
Large in females, they conduct eggs from the
ovaries to the outside.
- Urinary bladder: Thin membranous empty sac that holds the
urine; it opens into the cloaca.
- Cloaca: Chamber at the end of the rectum.
It receives wastes from the large intestine, urine from
the urinary bladder, and gametes .
It opens to the outside through the cloacal opening (anus)
4- The Circulatory system:
The heart: 3 chambers: 2 atria and 1 ventricle