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One practical way to see for yourself how an amphibian and reptile differ is to
compare the anatomy of two species, such as a frog and a
snake. Although you can observe the external anatomy on live ones at a pet store
or in the wild, it's hard to discover anything about their insides without doing a dissection.
Even if you don't want to dissect a snake (or a
another interesting reptile specimen), you might find the following description
of a snake's anatomy helpful. You can compare it to our
online frog dissection guide,
with pictures and detailed instructions. (You can also find
dissections online, instead of doing your own.) This is an
ideal project for junior high and high school students who are studying animal classification.
Click this link for a printable snake dissection diagram with labeled parts (.pdf).
Use this as a guide for locating organs.
- Inspect the external anatomy of the snake. Why do you think the
scales on the specimen's back (dorsal side) are different than the scales
on its belly (ventral side)? The ventral scales correspond to the number of
ribs that the snake has and allow greater flexibility of movement.
- Make a long incision down the center of the ventral surface, from the
cloacal opening to the throat. Carefully pull back the skin and pin it
down on either side, cutting the membrane layer underneath as necessary. Once
the snake is opened, observe how it looks inside. Then slice the
membrane away until it separates from the organs. (This membrane holds the
organs securely in place in the living snake.) This is the longest part of the
dissection process, but go slowly and cut carefully.
- Identify the major organs listed below. The heart, stomach,
gallbladder, liver, and large and small intestine will probably be the easiest
to find. These are listed in order roughly from head to tail.
Trachea: A dark-colored tube in throat that brings air to the lung.
Heart: Located just below trachea. It is a three-chambered like a frog
Right lung: Most snakes have only
one functioning lung, a long narrow sac starting near the heart. Look for it between the liver and stomach.
The specimen might also have another, smaller lung.
Liver: A long, thin orangish-colored organ on the left side (as you look at it).
Stomach: A long sac that connects to the esophagus in the throat and
small intestine lower down. Is your specimen's stomach empty or full? If full,
you might want to check out the contents to discover what the snake was eating.
Gallbladder & pancreas: The gallbladder is small and round,
usually greenish-colored from the bile for digestion stored in it. You might have to remove
the yellow fat bodies to see it. (A healthy snake will have many fat
bodies.) The pancreas looks just like an extension of the
intestine, right next to the stomach.
Small & large intestine: The small intestine starts right below the stomach and forms many coils.
Gonads: These might look similar to the
intestine, but are not connected to it. Male snakes are identifiable by
testes inside and hemipenes at the cloacal opening. Females have a pair of
ovaries and might have eggs. (If both the frog and snake specimens have eggs, be
sure to compare them!)
Kidneys: These are located near the end of the
large intestine; they should be similar in color to the intestine, but if you
look closely you'll see that they are a different kind of tissue.
Print out this diagram and fill in the labels yourself to test your
knowledge of snake anatomy:
See our other free dissection guides with photos and printable PDFs. Click here.
Don't be intimidated by dissection: watch our video with tips on getting started -- and enjoying it!