External Anatomy of the Frog

EXTERNAL ANATOMY OF THE FROG

Jeremy G. VicencioDepartment of Biology (UPM-CAS)

1st Semester, A.Y. 2010-2011

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Why do we study frogs?

1. They show both primitive and advanced vertebrate structures

2. The position of their internal organs is similar to that of humans

3. They are small and readily available

External Anatomy of the Frog


Part Description/Function

External nares Located near the snout or tip of the head, leads to the olfactory organs within

(Dorsal) Upper eyelid Immovable

(Ventral) Lower eyelid Can close over the entire eye

Nictitating membrane Movable translucent lower eyelid, protects the eye when the frog is underwater and serves to moisten the eye when it is on land

Browspot Located at the top of the head between the eyes which has the diameter of about a pin, a remnant of a median, light-sensitive eye that characterized primitive groups of fishes and amphibians

Tympanic membrane Disc-shaped area posterior to each eye, eardrum/outer ear



Cloacal aperture Combined orifice of the digestive and urogenital tracts at the posterior end of the trunk just dorsal to the junction of the hind legs

Forelimbs Emerge from the chest region behind the head, extends into three distinct regions: brachium (upper arm), antebrachium(forearm), manus (hand)

Manus Comprised of the carpus (wrist), metacarpus (palm), and four digits or fingers

Hindlimbs Emerge from the waist region and can be partitioned into: thigh(upper leg), shank/crus (lower leg), pes (long foot)

Foot Divided into tarsus (long ankle), metatarsus (instep), and five fully-webbed toes or digits

Prehallux or calcar Rudiment of the sixth missing toe, appears medially to the first toe as a small spur-like outgrowth



Vocal Sac Sound-resonating throat pouch of male frogs and toads. They are outpocketings of the floor of the mouth, or buccal cavity.

Toads vs. Frogs

Toads vs. Frogs

Males vs. Females

Males vs. Females

Males vs. Females

Males vs. Females

Male Vocal Sacs

Pithing of the frog

• Pithing is the destruction of the central nervous system by piercing the brain and/or spinal cord.

• This procedure is used in experiments to render the animal unconscious so that it feels no pain.

• Single-pithed frog – only the brain is destroyed

• Double-pithed frog – spinal cord is destroyed as well

Procedure

1. There are two accepted methods for pithing a frog.

2. One method of single pithing a frog entails holding the animal in a paper towel with its dorsal side up and with the index finger pressing the nose down so that the head makes a right angle with the trunk.

3. Locate the slight depression formed by the first vertebra and skull about 3 mm behind the line joining the posterior borders of the tympanic membrane. This groove represents the area of the foramen magnum.

4. Carefully insert a long, sharp-tipped needle or probe into the foramen magnum and direct it forward and a little downward.

5. Exert a steady pressure and rotate it, moving it from side to side in the cranial cavity to destroy the brain.

4. Carefully insert a long, sharp-tipped needle or probe into the foramen magnum and direct it forward and a little downward.

5. Exert a steady pressure and rotate it, moving it from side to side in the cranial cavity to destroy the brain.

6. To double pith the frog, insert the needle into the vertebral canal, directing it downward until it has reached the end of the canal. Move the needle from side to side as you go.

7. A second acceptable method to single pith a frog involves holding the animal in a paper towel with its dorsal side up and inserting one blade of a pair of scissors into the animal’s mouth and cutting off the top of the head just posterior to the eyes.

8. To double pith the animal, insert a long-sharp tipped needle or probe into the exposed vertebral column and direct it downward until it has reached the end of the canal, moving the needle from side to side as you go.

Procedure

Amitrano, R, & Tortora, GJ. (2007). Laboratory Exercises in Anatomy and Physiology with Cat Dissections

Pithing of the frog

Amitrano, R, & Tortora, GJ. (2007). Laboratory Exercises in Anatomy and Physiology with Cat Dissections

Documents

External Anatomy of the Frog