all about what no one wants to do :)

BACKGROUND INFORMATION


Snakes are reptiles, a group of animals that also includes alligators, crocodiles, lizards, turtles and tuataras. Herpetologists study reptiles as well as amphibians.

Snakes are cold-blooded, or ectothermic, meaning that their bodies rely on the sun and heat to regulate their body temperatures. Their bodies are covered with overlapping scales made out of keratin, which is what our fingernails are made from. The scales are shed as the snake grows and help snakes hold in moisture. We, as humans, lose our skin cells too, but not all at one time like snakes.

Snakes are in the class Reptilia, which are in the phylum Chordata, meaning that they are vertebrates, animals with backbones. Humans have 32 vertebrae, while snakes have at least 100 vertebrae. Some have as many as 400! The flexibility of a snake’s jaw allows it to engulf larger animals. This is due to the fact that the jaws are not rigidly attached to its skull.
As with other reptiles, snakes possess a cloaca, an internal chamber that receives wastes from the digestive system and eggs or sperm from the reproductive system before they leave the body. Snakes do not have a urinary bladder; instead, they excrete all their waste through their cloaca.

There are many misconceptions about snakes, mainly based upon unnecessary fears that individuals have about these reptiles. In fact, there are only five types of venomous snakes in Missouri, while there are 33 nonvenomous types.

Like other animals, snakes have defense mechanisms that range from their camouflage color patterns, mimicking other color patterns, venom, hissing, and rattling its tale. Even though snakes don’t have legs, their efficient method of locomotion through lateral undulation, or serpentine movement, rectilinear locomotion, serpentine and sidewinding, aids in their quick get-a-way. Each of these different styles of movement requires specific way of tightening and relaxing a set of muscles on each side of its body.

EXTERNAL ANATOMY


1). Compare the dorsal scales to the ventral scales on your snake. Describe the difference in the space below, and explain how you account for the difference in structure between these scale types. Examine a dorsal scale with your digital microscope and draw and measure it in cm. (Question 1)



2). Does your snake have eyelids? A nictitating membrane? What is the function of this structure? (Question 2)



3). Before you actually dissect the snake, cut off a small chunk of skin of the dorsal side so you can example the muscle underneath. Draw the external muscle tissue below. (Question 3)

4). Measure the length of your snake in cm. (Question 4)

5). Cut into the jaw and identify the structures labeled on the diagram. Confirm these with Mrs. Nash, and she will check them on your dissection sheet.
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INTERNAL ANATOMY


Use this website as your resource guide.

The site will specifically direct you concerning the method you use to dissect your snake. Use the image below to help you identify the snake organs. These are the ones that you will identify with me for points on your dissection guide.

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In the first quarter of the snake are the trachea (yellow arrow), thyroid (T), jugular vein (blue arrow), carotid artery (red arrow) and heart (H).
In the first quarter of the snake are the trachea (yellow arrow), thyroid (T), jugular vein (blue arrow), carotid artery (red arrow) and heart (H).



Found in the fourth quarter of the snake are the adrenals (A), a testis (T) and the right kidney (K).
Found in the fourth quarter of the snake are the adrenals (A), a testis (T) and the right kidney (K).


Found in the tail region are the large intestine (Li), cloaca (Cl), vent (V), vestigial pelvic limbs or spurs (green arrow), hemipenes (yellow arrows), and scent gland (red arrow).
Found in the tail region are the large intestine (Li), cloaca (Cl), vent (V), vestigial pelvic limbs or spurs (green arrow), hemipenes (yellow arrows), and scent gland (red arrow).

This site will help you with internal organ identification. All other questions are on your lab guide.