Internal Anatomy - Frog Dissection Manual

Materials

1. frog
2. dissecting pan
3. scissors
4. forceps
5. probe

Structures Inside the Mouth

1. Open the mouth using your fingers or forceps.
2. Use the scissors to cut the back of the mouth where the mandible attaches to the maxilla.
3. When done, you should be able to easily open the mouth to examine these internal mouth structures.

• mandible – the lower jaw maxilla – the upper jaw
• maxillary teeth – a row of teeth found on the margin of the maxilla
• vomerine teeth – two small patches (bumps) of teeth found on the roof of the mouth in the center of the anterior area internal nares – the nostril openings on the roof of the mouth just lateral to the vomerine teeth
• eye sockets – on the roof of the mouth where the eyes bulge inward
• Eustachian tubes – the openings for these tubes are found on each side of the roof of the mouth near the hinge of the jaws esophagus – the opening for this tube is at the back of the mouth (it leads down the throat to the stomach)
• glottis – this is the opening for the trachea; it is just anterior to the opening of the esophagus on the floor of the mouth tongue – found on the floor of the mouth; hinged at its anterior end
• buccal cavity – the inside cavity of the mouth

Structures of the Hindlimbs

1. Remove the skin from one of the hindlimbs.
2. Remove the thigh muscles from the femur and the calf muscles from the tibiofibula.

• thigh muscles – the muscles of the thigh (uppermost section of the hindlimb)
• calf muscles – the muscles of the shank (middle section of the hindlimb)
• femur – the bone running through the thigh
• tibiofibula – the bone running through the shank
• Achilles tendon – the tendon that connects the calf muscles to the foot (white in color)

Structures of the Coelom

1. Place the frog on its back.
2. Using the forceps, lift the skin of the lower abdomen and make a cut with the scissors.
3. Insert the scissors into the slit and make a cut from near the cloacal opening to below the lower jaw.
4. Make shallow cuts to the sides just posterior to the forelimbs and anterior to the hindlimbs.
5. Make similar cuts through the body wall if the previous cuts did not already do so.
6. Cut off the flaps to reveal the organs inside the coelom.
7. Remove the following organs and lay them on your tray for identification.
8. Note: leave the stomach, small intestine, and large intestine attached to each other when you remove them.

• heart (atria and ventricle) – in the center at the anterior end between the forelimbs; atria – red brown, ventricle - white liver – on both sides of the heart; contains three lobes (sections); largest organ in body; brownish to greenish
• gall bladder – under the liver and attached to it; small round sac; yellow-green and slightly transparent
• esophagus – attached to back of throat and stomach; cut as high up as you can; do not separate from stomach; white stomach – widest part of digestive tract; very muscular; white
• small intestine – extends from stomach to large intestine; smaller diameter than large intestine; white large intestine – extends from small intestine to cloaca; larger diameter than small intestine; white cloaca – the very end of the digestive tract; cut as low down as you can; white
• mesentery – the connective tissue holding the different areas of the small intestine together; very thin but strong; clear spleen – round body similar in size to the heart; found in the mesentery; makes red blood cells; dark reddish brown lungs – to the right and left of the heart underneath the liver; spongy sacs; color varies – dark gray to reddish brown kidneys – long, flat structures along the dorsal surface of the coelom near the posterior end of the cavity; dark brown fat bodies/ovaries – yellow or brown wormlike structures in the mid abdominal area (ovaries are too small to see)
• fat bodies/testes – yellow or brown wormlike structures in the mid abdominal area (testes will be small, oval and white)