Frog dissecting | PPT

Anatomy and Dissection Overview

Frog anatomical dissection encompasses four primary investigative regions: the oral cavity (buccal cavity), external musculature categorized by dorsal and ventral orientations, deep muscular structures revealed via layered dissection, and internal visceral organs across male and female specimens.

Dissection procedures systematically isolate superficial layers before advancing to deep musculoskeletal and coelomic systems to permit exact structural identification and bilateral comparison.

Cephalic and Pectoral Girdle Musculature

Muscles of the head, neck, and shoulder regions operate jaw mechanics and forelimb mobilization. Key surface landmarks and muscle groups include:

  • Tympanic membrane: The external auditory structure positioned posteriorly to the ocular orbit.

  • Masseter (4): Muscle located ventrolateral to the eye, involved in jaw elevation and closure.

  • Depressor mandibularis (5): Positioned posterior to the tympanic ring; functions to depress the lower jaw and open the mouth.

  • Dorsalis scapulae (6): Located over the suprascapular cartilage; mediates shoulder positioning and foreleg retraction.

  • Latissimus dorsi (10): Broad, triangular dorsal muscle lying posterior to the dorsalis scapulae, functioning in forelimb retraction.

  • Pterygoideus (2): Deep cranial muscle situated medial and anterior relative to the jaw articulation.

  • Temporal (3): Dorsal cranial muscle located medial to the masseter and eye.

  • Deltoid (7): Anterior pectoral/shoulder muscle responsible for forelimb flexion and adduction.

Trunk and Abdominal Musculature

Trunk musculature maintains hydrostatic body wall pressure, supports posture, and assists in pulmonary ventilation.

Dorsal Trunk

  • Longissimus dorsi (11): Extends longitudinally along the vertebral column to extend and flex the spine.

  • External oblique (14): Forms the lateral and ventrolateral body wall, compressing internal viscera.

Ventral Trunk

  • Mylohyoid / Mylohoid (1 / 30): Broad, thin transverse muscle spanning the intermandibular space to elevate the floor of the mouth during respiration.

  • Pectoralis (9): Large fan-shaped ventral chest muscle facilitating humerus adduction.

  • Rectus abdominis (12): Long longitudinal ventral abdominal muscle flanking the midline.

  • Linea alba (13): Medial longitudinal band of fibrous connective tissue separating the paired rectus abdominis bands along the ventral midline.

  • Cutaneous abdominis (15): Thin abdominal sheet situated between deeper musculature and the integument.

Pelvic and Hindlimb Musculature

Hindlimb musculature provides propulsion for swimming and jumping, organized into lateral, medial, superficial, and deep groupings.

Lateral Hindlimb Musculature

  • Gluteus (17): Deep dorsal pelvic muscle that abducts and rotates the thigh.

  • Piriformis (18): Small posterior pelvic muscle located near the cloaca.

  • Triceps femoris (20): Massive, three-headed muscle covering the anterior and lateral surface of the thigh; acts as the primary extensor of the lower limb (shank).

  • Biceps femoris (29): Narrow muscular band situated along the posterolateral aspect of the thigh.

  • Semimembranosus (28): Large muscle forming the posterior border of the dorsal thigh, also identified structurally as Semimembranous.

  • Gastrocnemius (26): Large calf muscle along the posterior shank; functions as a powerful ankle extensor and knee flexor.

  • Tendon of Achilles / Tendon Achilles (27): Strong distal connective tendon of the gastrocnemius spanning across the ankle.

Medial Hindlimb Musculature (Superficial)

  • Sartorius (22): Narrow, superficial longitudinal strap traversing obliquely across the ventral thigh; flexes the leg and adducts the thigh.

  • Adductor longus (19): Positioned immediately deep and adjacent to the sartorius.

  • Adductor magnus (21): Large triangular muscle situated medial to the sartorius and anterior to the gracilis complex; functions in strong thigh adduction.

  • Gracilis major (24): Broad, medial muscle situated along the posterior margin of the ventral thigh.

  • Gracilis minor (25): Thin superficial muscular strip running along the posterior edge of the gracilis major.

Medial Hindlimb Musculature (Deep Dissection)

Deep identification requires transecting superficial structures:

  • Sartorius (cut): Reflects to expose the underlying adductor longus and adductor magnus.

  • Adductor longus (cut): Reflects to display the anterior pelvic insertions.

  • Semitendinosus (23): Characterized by a distinctive double belly structure; situated deeply between the gracilis major and adductor magnus.

Master Muscle Reference Key

Standard numerical indexing used in frog muscle identification:

  • 1: Mylohyoid

  • 2: Pterygoideus

  • 3: Temporal

  • 4: Masseter

  • 5: Depressor mandibularis

  • 6: Dorsalis scapulae

  • 7: Deltoid

  • 8: Triceps brachii

  • 9: Pectoralis

  • 10: Latissimus dorsi

  • 11: Longissimus dorsi

  • 12: Rectus abdominis

  • 13: Linea alba

  • 14: External oblique

  • 15: Cutaneous abdominis

  • 16: ---- [Unassigned]

  • 17: Gluteus

  • 18: Piriformis

  • 19: Adductor longus

  • 20: Triceps femoris

  • 21: Adductor magnus

  • 22: Sartorius

  • 23: Semitendinosus

  • 24: Gracilis major

  • 25: Gracilis minor

  • 26: Gastrocnemius

  • 27: Tendon Achilles

  • 28: Semimembranous

  • 29: Biceps femoris

Oral Cavity Structures

The internal oral cavity features specialized adaptations for capturing and ingesting prey:

  • 30. Maxillary teeth: Fine, sandpaper-like teeth embedded along the rim of the upper jaw (maxilla).

  • 31. Vomerine teeth: Paired patches of pointed structures projecting from the roof of the mouth (vomer bones).

  • 33. Eustachian tubes: Lateral apertures on either side of the pharynx communicating with the inner tympanic cavities.

  • 34. Tongue: Muscular structure attached at the anterior floor of the jaw; flips forward to capture prey.

  • 35. Glottis: Longitudinal slit on the pharyngeal floor leading directly into the laryngotracheal chamber.

  • 36. Esophagus: Wide opening at the posterior terminus of the buccal cavity providing entry to the stomach.

Internal Viscera and Circulatory Anatomy

Opening the coelomic cavity exposes the organ systems comprising the circulatory, digestive, and excretory complexes:

Cardiovascular and Respiratory Organs

  • Ventricle (38 / 39): Thick-walled, conical muscular pumping chamber at the apex of the three-chambered heart.

  • Auricle (atrium) (38 / 39): Paired thin-walled chambers (left and right atria) receiving venous blood.

  • Conus arteriosus (40): Thick arterial vessel arising ventrally from the ventricle that directs blood into systemic and pulmocutaneous flow.

  • Aortic arches (41): Bilateral paired vessels branching from the truncus/conus system to distribute blood.

  • Lung (42): Paired, thin-walled saccular respiratory organs lined with vascularized pockets.

Digestive and Excretory Organs

  • Liver (43): Multi-lobed, prominent dark organ occupying the anterior ventral body cavity; produces bile and processes metabolites.

  • Gall bladder (44): Small green-tinted sac tucked within liver lobes for bile storage.

  • Fat bodies (51): Finger-like, yellow, lipid-rich projections located anterior to the kidneys and gonads; provide energy reserves during hibernation and reproduction.

  • Urinary bladder (52): Thin, bilobed, membranous pouch attached ventrally near the cloaca.

  • Spleen (49): Small, round reddish lymphoid organ embedded in the dorsal mesentery.

  • Kidney (50): Paired elongated, retroperitoneal organs lying against the dorsal coelomic wall.

Sex-Specific Urogenital and Visceral Anatomy

Internal visceral configurations vary between sexes in reproductive architecture and associated retention structures:

Shared Visceral Structures

  • 45. Stomach: Curved muscular organ extending from the esophagus for chemical and mechanical digestion.

  • 46. Small intestine: Coiled tubular conduit receiving chyme from the stomach.

  • 47. Large intestine: Broad terminal segment of the alimentary canal terminating at the cloaca.

  • 48. Pancreas: Irregular glandular mass situated within the mesentery between the stomach and duodenum.

  • 49. Spleen: Circulatory reservoir located in the posterior mesentery.

  • 50. Kidney: Excretory organ positioned along the subvertebral lymph spaces.

  • 55. Adrenal gland / Adrenal: Yellowish endocrine strip situated along the ventral surface of each kidney.

Male Internal Anatomy

  • 56. Testis: Paired oval, creamy-yellow gonads situated along the ventral borders of the anterior kidneys.

  • 57. Vestigial oviducts: Slender, wavy paired ducts retained along the lateral margins of the coelom despite non-functional reproductive status.

Female Internal Anatomy

  • 51. Fat bodies: Extensively developed clusters supporting reproductive energetics.

  • 52. Urinary bladder: Ventral waste fluid repository.

  • 58. Ovary: Paired lobular organs containing pigmented ova, which swell significantly during breeding condition.

  • 59. Oviduct: Long, highly convoluted white tubes running along the dorsal coelom that transport eggs and secrete jelly coats before deposition into the cloaca.