Vertebrate Skeleton Functions and Types

The Skeleton of Vertebrates

• The skeleton provides support, a surface for muscle attachment, calcium for the blood, and a site for blood cell formation.
• There are two types of skeletons: exoskeleton (hardened bony or horny structures that provide external protection) and endoskeleton (consists of bone and cartilage).

The Endoskeleton of Frogs/Toads

• The endoskeleton is almost entirely composed of bone and cartilage.
• It can be divided into two parts: axial endoskeleton (structures located at the center of the body) and appendicular endoskeleton (structures located in the extremities).

Axial Endoskeleton

• Skull: flattened dorsoventrally, wider posteriorly, and narrower anteriorly.
• Skull components:
  • Nasal bones: flat, triangular-shaped bones on the dorsal surface of the skull.
  • Frontoparietals: long, slender, flat bones that cover most of the brain.
  • Foramen magnum: large opening at the posterior end of the skull through which the spinal cord passes.
  • Exoccipital: bone that surrounds the posterior part of the brain.
  • Occipital condyles: prominent bones that project from the exoccipital.
  • Upper jaw: formed by the premaxillae, maxillae, and quadratojugals.
  • Premaxillae: short, teeth-bearing bones that form the anterior most edge of the upper jaw.
  • Maxillae: curved, teeth-bearing bones that form the margin of the jaw.
  • Quadratojugals: short bones that make up the posterior part of the upper jaw.
  • Squamosals: bones that extend upward from the quadratojugals and serve as a brace between the cranium and the posterior portion of the jaws.

Vertebral Column

• Composed of 10 vertebrae.
• Specialized for the shortening of the trunk of the body.
• Atlas: first vertebra, specialized for articulation with the skull.
• Urostyle: represents several fused tail or caudal vertebrae, has a conspicuous dorsal keel, and a hollow canal.

Pectoral and Pelvic Girdles

• Pectoral girdle: consists of a series of bones and cartilages that encircle the body and provide support for the forelimbs.
• Pelvic girdle: consists of two identical halves, each called an innominate bone, and supports the hindlimbs.

Bones of the Forelimbs and Hindlimbs

• Forelimbs:
  • Humerus: bone of the upper arm.
  • Radio-ulna: fusion of the radius and ulna.
  • Carpals: bones of the wrist.
  • Metacarpals: bones of the hand.
  • Phalanges: smaller bones of the digits.
• Hindlimbs:
  • Femur: bone of the thigh.
  • Tibiofibula: fusion of the tibia and fibula.
  • Tarsals: bones of the ankle.
  • Metatarsals: bones of the sole.
  • Phalanges: smaller bones of the digits.

Skeletal Muscles

• Important hints for dissection:
  • Separate muscle bundles from each other.
  • Observe the direction of the fibers and the extent of the muscle.
  • Use a blunt instrument to loosen the muscle tissues.
  • Never cut muscles unless instructed to do so.
• Muscles of the head and trunk:
  • Mylohyoid: thin, broad, transversely oriented fibers.
  • Sternoradialis: thick, median pair of muscles.
  • Cutaneous pectoralis: most ventral, thin, pocket-like superficial muscle.
  • Pectoralis: fan-shaped muscles posterior to the sternoradialis.
  • Rectus abdominis: longitudinal muscle lateral to the linea alba.
  • External oblique: sheet-like muscle lateral to the rectus abdominis.
• Muscles of the thigh and shank:
  • Sartorius: flat, strap-like muscle.
  • Adductor longus: slender muscle.
  • Adductor magnus: thick muscle near the groin area.
  • Gracilis major: large muscle with oblique fibers.
  • Gastrocnemius: large muscle situated at the back of the shank.
  • Tibialis posticus: long, narrow, but thick muscle anterior to the gastrocnemius.
  • Tibialis anticus: most anterior muscle of the shank, which can also be seen dorsally.

The Skeleton of Vertebrates

• The skeleton provides support, a surface for muscle attachment, calcium for the blood, and a site for blood cell formation.
• There are two types of skeletons: exoskeleton (hardened bony or horny structures that provide external protection) and endoskeleton (consists of bone and cartilage).

The Endoskeleton of Frogs/Toads

• The endoskeleton is almost entirely composed of bone and cartilage.
• It can be divided into two parts: axial endoskeleton (structures located at the center of the body) and appendicular endoskeleton (structures located in the extremities).

Axial Endoskeleton

• Skull: flattened dorsoventrally, wider posteriorly, and narrower anteriorly.
• Skull components:
  • Nasal bones: flat, triangular-shaped bones on the dorsal surface of the skull.
  • Frontoparietals: long, slender, flat bones that cover most of the brain.
  • Foramen magnum: large opening at the posterior end of the skull through which the spinal cord passes.
  • Exoccipital: bone that surrounds the posterior part of the brain.
  • Occipital condyles: prominent bones that project from the exoccipital.
  • Upper jaw: formed by the premaxillae, maxillae, and quadratojugals.
  • Premaxillae: short, teeth-bearing bones that form the anterior most edge of the upper jaw.
  • Maxillae: curved, teeth-bearing bones that form the margin of the jaw.
  • Quadratojugals: short bones that make up the posterior part of the upper jaw.
  • Squamosals: bones that extend upward from the quadratojugals and serve as a brace between the cranium and the posterior portion of the jaws.

Vertebral Column

• Composed of 10 vertebrae.
• Specialized for the shortening of the trunk of the body.
• Atlas: first vertebra, specialized for articulation with the skull.
• Urostyle: represents several fused tail or caudal vertebrae, has a conspicuous dorsal keel, and a hollow canal.

Pectoral and Pelvic Girdles

• Pectoral girdle: consists of a series of bones and cartilages that encircle the body and provide support for the forelimbs.
• Pelvic girdle: consists of two identical halves, each called an innominate bone, and supports the hindlimbs.

Bones of the Forelimbs and Hindlimbs

• Forelimbs:
  • Humerus: bone of the upper arm.
  • Radio-ulna: fusion of the radius and ulna.
  • Carpals: bones of the wrist.
  • Metacarpals: bones of the hand.
  • Phalanges: smaller bones of the digits.
• Hindlimbs:
  • Femur: bone of the thigh.
  • Tibiofibula: fusion of the tibia and fibula.
  • Tarsals: bones of the ankle.
  • Metatarsals: bones of the sole.
  • Phalanges: smaller bones of the digits.

Skeletal Muscles

• Important hints for dissection:
  • Separate muscle bundles from each other.
  • Observe the direction of the fibers and the extent of the muscle.
  • Use a blunt instrument to loosen the muscle tissues.
  • Never cut muscles unless instructed to do so.
• Muscles of the head and trunk:
  • Mylohyoid: thin, broad, transversely oriented fibers.
  • Sternoradialis: thick, median pair of muscles.
  • Cutaneous pectoralis: most ventral, thin, pocket-like superficial muscle.
  • Pectoralis: fan-shaped muscles posterior to the sternoradialis.
  • Rectus abdominis: longitudinal muscle lateral to the linea alba.
  • External oblique: sheet-like muscle lateral to the rectus abdominis.
• Muscles of the thigh and shank:
  • Sartorius: flat, strap-like muscle.
  • Adductor longus: slender muscle.
  • Adductor magnus: thick muscle near the groin area.
  • Gracilis major: large muscle with oblique fibers.
  • Gastrocnemius: large muscle situated at the back of the shank.
  • Tibialis posticus: long, narrow, but thick muscle anterior to the gastrocnemius.
  • Tibialis anticus: most anterior muscle of the shank, which can also be seen dorsally.

The Skeleton

• The skeleton serves as support or framework for the softer parts of the body, provides a firm surface for the attachment of muscles, supplies calcium to the blood, and is an important site in the formation of blood cells.
• There are two types of skeleton: exoskeleton and endoskeleton.
• The exoskeleton of vertebrates consists of hardened bony or horny structures that develop in the skin and provides external protection to the animal.
• The skeleton of the frog/toad is almost entirely endoskeletal in nature and consists almost entirely of bone and cartilage.

Musculo-Skeletal System

• Muscles and skeleton are often considered together as a functional unit that permit body movements and locomotion.
• Muscles are attached to the bones by a connective tissue called tendon.
• A broad, flat, and sheet-like tendon is called aponeurosis.
• Skeletal muscles often have two points of attachment, and the part in between is sometimes referred to as the belly of the muscle.

Gross Anatomy of the Toad Skeleton

• The skeleton of the toad can be divided into axial and appendicular endoskeleton based on position in the body.
• Axial endoskeleton consists of:
  • Skull
  • Visceral skeleton
  • Vertebral column and ribs
  • Sternum
• Appendicular endoskeleton consists of:
  • Girdles (pectoral and pelvic)
  • Bones of the limbs (anterior and posterior)

Skull

• The skull of the frog is flattened dorsoventrally and is wider posteriorly and narrower anteriorly.
• It encloses the brain and the sense organs.
• The skull consists of:
  • Cranium (braincase)
  • Visceral skeleton (jaws, hyoid apparatus, and bones of the ears)
• Notable features of the skull include:
  • Nasal bones
  • Frontoparietals
  • Foramen magnum
  • Exoccipital
  • Occipital condyles
  • Upper jaw (premaxillae, maxillae, and quadratojugals)
  • Squamosals

Vertebral Column

• The vertebral column of a frog is very specialized due to the shortening of the trunk of the body.
• It consists of ten vertebrae.
• Notable features of the vertebral column include:
  • Atlas (specialized for articulation with the skull)
  • Urostyle (represents several fused tail or caudal vertebrae)

Pectoral and Pelvic Girdles

• The pectoral girdle consists of a series of bones and cartilages that encircle the body and provide support for the forelimbs.
• The pelvic girdle supports the hindlimbs.

Bones of the Limbs

• The bones of the forelimbs include:
  • Humerus (upper arm)
  • Radioulna (fusion of radius and ulna)
  • Carpals (wrist bones)
  • Metacarpals (bones of the hand)
  • Phalanges (smaller bones of the digits)
• The bones of the hindlimbs include:
  • Femur (thigh bone)
  • Tibiofibula (fusion of tibia and fibula)
  • Tarsals (ankle bones)
  • Metatarsals (bones of the foot)
  • Phalanges (smaller bones of the digits)

Skeletal Muscles of the Toad

• Skeletal muscles can be divided into ventral and dorsal muscles based on their location.
• Notable ventral muscles include:
  • Mylohyoid
  • Sternoradialis
  • Cutaneous pectoralis
  • Pectoralis
  • Rectus abdominis
  • External oblique
• Notable dorsal muscles include:
  • Longissimus dorsi
  • Iliolumbaris
  • Coccygeo-iliacus
  • Triceps femoris
  • Gluteus
  • Biceps femoris (or Iliofibularis)
  • Semimembranosus
  • Gastrocnemius
  • Peroneus
  • Tibialis anticus

Visceral Skeleton

• Consists of upper and lower jaws, hyoid apparatus, and cartilages that support the ventral wall of the larynx or voice box in frogs

Vertebral Column

• Composed of ten vertebrae in frogs
• First vertebra (atlas) is specialized for articulation with the skull
• Atlas lacks transverse processes, which are present on other vertebrae
• Vertebral column is continued beyond the sacral region by the urostyle, which represents several fused tail or caudal vertebrae
• Urostyle has a conspicuous dorsal keel and a hollow canal

Pectoral Girdle

• Consists of a series of bones and cartilages that encircle the body and provide support for the forelimbs
• Firmly attached to the sternum or breastbone in toads

Pelvic Girdle

• Supports the hindlimbs
• Consists of two identical halves, one half of which is called an innominate bone

Bones of the Forelimbs

• Humerus is the bone of the upper arm
• Radioulna is the fusion of two bones, the radius and ulna of other land vertebrates
• Olecranon is a process that serves for the attachment of muscles

Skull

• Upper jaw formed by premaxillae, maxillae, and quadratojugals
• Premaxillae are paired, short, teeth-bearing bones that form the anterior most edge of the upper jaw
• Maxillae are paired, curved teeth-bearing bones that form the margin of the jaw
• Quadratojugals are short bones that make up the posterior part of the upper jaw but do not bear teeth
• Squamosals are bones that extend upward from the quadratojugals and serve as a brace between the cranium and the posterior portion of the jaws to support the cartilaginous auditory region

Ventral View of the Skull

• Vomers are two flat, wing-shaped bones in the roof of the mouth just posterior to the premaxillae
• Palatines are slender, rod-like bones that extend laterally from near the median line to the maxillae
• Parasphenoid is a single, dagger-shaped bone that forms the floor of the cranium

Functions of the Skeleton

• Serves as support or framework for the softer parts of the body
• Provides a firm surface for the attachment of muscles used in movement and locomotion
• Supplies calcium to the blood
• Important site in the formation of blood cells

Learn about the essential functions of the skeleton in vertebrate animals, including support, muscle attachment, and blood cell formation. Discover the two types of skeletons.