LABORATORY 6

CHORDATA, VERTEBRATA, ANIMALIA

Dissection of the Frog:  Rana catesbiana

 

In this laboratory you will perform the dissection of the frog.  The frog is representative of lower vertebrates.  You will compare this organism and its internal structure with another vertebrate mammal -- the fetal pig -- during your laboratory next week. 

 

Amphibians were the first tetrapods.  Though there are many differences, a great deal of the knowledge gained from the study of the frog is applicable to the human body.  As you work this week on the frog and next week on the pig, think actively about similarities and differences compared with your own body.   

 

EXTERNAL FEATURES

 

These bullfrogs, Rana catesbiana, have been preserved and contain red and blue latex injected into the circulatory system for easier recognition of major vessels.  Which vessels are injected with red latex ? An incision has been made in your specimen for this purpose.  First, observe the external features of your specimen.  Identify the mouth, external nares, eyes, eyelids, and tympanic membrane on the head.  There are two pairs of limbs on the trunk :  the short forelimb consisting of the arm, forearm, and hand with four digits, and the muscular hindlimb consisting of a thigh, leg, and foot with five digits. Also observe the cloacal opening.  Externally, the male can be distinguished from the female by the enlarged pad on the innermost finger.

 

MOUTH CAVITY

 

Pry open the mouth and rinse if necessary.  Locate the following structures:  the maxillary teeth on the margin of the upper jaw; the vomerine teeth on the palate which are used for holding food, not for mastication, the internal nares; the Eustachian aperture opening into the auditory tube; the large transverse slit opening into the esophagus; the glottis opening into the trachea and leading to the lungs; the vocal sac apertures in the male: and the fleshy tongue.

 

GENERAL INTERNAL ANATOMY

 

Prepare to open the abdominal and thoracic cavities by raising the skin on the ventral surface and making a longitudinal cut through the skin from the pelvis to the tip of the lower jaw.  Make short transverse cuts at the anterior and posterior ends of the trunk and fold back the flaps of skin.

 

Before continuing the dissection, not the following muscles:  the external oblique, the pectoralis, and the rectus abdominus.  Also find the linea alba -- a white stripe that makes the position of the ventral abdominal vein.  make a longitudinal incision a little to one side of the linea alba through the body wall including the sternum, to the posterior end of the lower jaw.  Be careful not to injury the abdominal and the internal organs within the coelom. 

 

DIGESTIVE AND RELATED ORGANS

 

Using the picture in your Atlas on page 182, identify the following: the three lobes of the liver, the gall bladder, the bile duct, the esophagus, the stomach, the pylorus, the pancreas, the duodenum, the ileum, the large interstice,  the urinary bladder, the cloaca, the spleen, and the mesentery which supports the various organs.  The cloaca is a common depository for the products of the digestive, urinary, and reproductive systems.  It is seen in all vertebrates except most mammals.  Also, note the heart within the pericardium and the pair of lungs. 

 

UROGENITAL ORGANS

 

In the female frogs, note the large ovaries, the coiled oviducts, the yellow fat bodies, the kidneys, and the bilobed urinary bladder.  There may be numerous eggs contained with the ovaries. In the male, note the testes, and the fat bodies, the kidneys, and the bladder.   The testis is a small spherical organ in males, which rests on the kidneys.

 

SKELETON

 

Observe the skeletons.  Compare the frog skeleton (Atlas p. 178) with the human skeleton.  Both the frog skeleton and the human skeleton are divided into the 1) axial skeleton, which consists of the skull and vertebral column and 2) the appendicular skeleton which consists of the pectoral girdles and bones of the arms and the pelvic girdle and the bones of the legs.  The vertebral column consists of 10 bones.  There is one cervical vertebrae: the atlas, which articulates with the cranium.  The next seven bones are the abdominal vertebrae, then the sacrum, which is followed by the last and longest vertebral bone -- the urostyle. Locate and be able to identify these bones on the frog:

 

       

Cranium

atlas

carpals

phalanges

metacarpals

metatarsals

Humerus

clavicle

scapula

Sacrum

calcar

urostyle

astragalus

radio-ulna

calcaneum

Femur

sacral vertebra

 

                                            

MUSCLES

 

Remove the skin from one arm and leg your specimen.  note the smooth glass appearance of the musculature, which covers the skeleton.  Locate the following muscles in your Atlas. 

 

       

deltoid

triceps femoris                    

gluteus

Myohyoid

gastronemius       

external abdominal oblique

pectoralsis

Tendon of Achilles (tendo calcaneus)

latissimus dorsi     

 

 

 

CIRCULATORY SYSTEM

Using the illustrations in your Atlas on page 183, locate the following components of the circulatory system:

 

       

Ventricle

aortic arches

hepatic vein

posterior vena cava

systemic arch

subclavian artery

ventral abdominal vein

femoral veins

pelvic veins

common iliac arteries

renal arteries

subclavian vein

renal vein

 

 

 

 

You may view and review the video on Dissection of the Frog in the LRC.  Remember to bring your dissection kits.  Latex gloves will be provided for all dissections.  Make certain to dispose of all dissected materials as directed by your instructor.  Rinse dissecting trays thoroughly and stack them so that they will air dry for the next usage.

 

Your lab report should include title, date, organism (genus, species, and common name), a list of systems to be studied and the organs of that system to be identified.  Descriptive information about new or unfamiliar organs should be included.  Indicate textbook, Atlas, etc. references for pictures and diagrams specifically by page number.  Write a paragraph about your dissection experience.  Who did you work with?  What did you expect?  What was unexpected?  How well did this facilitate your understanding of the interdependence between the body systems?  Were you dreading this dissection lab?  Are you comfortable with the procedure?  In other words, tell me what you think and how you feel about your laboratory experience.