External Anatomy

1. Place the frog on the dissecting pan. Do not pin it down.
2. Use these descriptions and the picture to identify each of the following external structures.

A.

• Head – the anterior end of the frog extending to and including the eardrums
• mouth – the large opening at the anterior end of the head made up of a maxilla and mandible maxilla – the upper jaw bone
• mandible – the lower jaw bone
• external nares (i.e. nostrils) – two small openings on the dorsal surface of the head near the tip eyes – two eyes protrude from the head just posterior to the external nares
• nictitating membrane – an extension of the lower eyelid that can come up to protect the eye tympanum (i.e. eardrum) – round membranes just posterior and ventral to the eyes

B.

• Trunk – the posterior end of the frog extending from the head to the hindlimbs
• cloacal opening – the hole at the posterior end of the frog (it’s the anus but has more functions)

C.

• Appendages – the limbs that extend from the trunk including the forelimbs and hindlimbs forelimbs – short extensions from the anterior end of the trunk
• arm – the uppermost section of the forelimb extending from the shoulder to the elbow forearm – the middle section of the forelimb extending from the elbow to the wrist hand – the lowermost section of the forelimb extending outward from the wrist
• hindlimbs – long extensions from the posterior end of the trunk
• thigh – the uppermost section of the hindlimb extending from the hips to the knee shank – the middle section of the hindlimb extending from the knee to the ankle foot – the lowermost section of the hindlimb extending outward from the ankle
• digits – the fingers and toes; note: there are four finger digits but five toe digits

D.

• Skin – the outer covering of the head, truck, and appendages; it is smooth and moist epidermis – the outer layer of the skin containing
• pigment granules for coloration dermis – the skin layer under the epidermis containing chromatophores (i.e. pigment cells)