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Questions and Answers
How many visceral arches are present in gnathosomes?
How many visceral arches are present in gnathosomes?
What is the name of the cartilage that forms the lower jaw?
What is the name of the cartilage that forms the lower jaw?
What is the function of the succeeding arches after the second visceral arch?
What is the function of the succeeding arches after the second visceral arch?
How many dermal elements are divided into?
How many dermal elements are divided into?
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What is the function of the roofing bones?
What is the function of the roofing bones?
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Which type of fish has a series of paired and unpaired bones extending along the midline from the nares to the occiput?
Which type of fish has a series of paired and unpaired bones extending along the midline from the nares to the occiput?
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What is the name of the bones that form the upper jaw?
What is the name of the bones that form the upper jaw?
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Which visceral arch is also known as the mandibular arch?
Which visceral arch is also known as the mandibular arch?
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What is the name of the cartilage that forms the upper jaw and is located dorsally?
What is the name of the cartilage that forms the upper jaw and is located dorsally?
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How many paired segments are present per arch in gnathosomes?
How many paired segments are present per arch in gnathosomes?
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Study Notes
Chondrocranium
- Formed by the fusion of prechordal plates, which remain free and widely separated in lower vertebrates with broad heads (platytrabic condition)
- Sometimes joined by a plate of cartilage and fused at the anterior end to form a Y-shaped structure (tropitrabic condition)
- Composed of various elements distinct in the embryo, including the notochord, prechordal cartilage or trabeculae cranii, and parachordal cartilages
Basal Plate
- Formed by the merger of parachordal cartilages above, below, or around the notochord
- Anterior part of the plate encloses a large cavity with lateral edges pierced by foramina for the passage of cranial nerves
- Posterior part of the plate has two or more projections called occipital condyles, which articulate with the first vertebra of the spine
Neural Arches and Sense Capsule
- Neural arches arise from the posterior angles of the basal plate to encircle the spinal cord at the point where it enters the skull
- Sense capsule houses the nasal chambers and inner ear, and joins the anterior ends of the trabeculae cranii
- Otic (auditory) capsules join the margins of the occipital arch
- Eye capsules remain free to allow for independent movement of the eyes
Visceral Skeleton
- Skeleton of the pharyngeal pouches in vertebrates, modified to perform new functions on land
- In fishes, it is the skeleton of the jaws and gill arches
- In jawless vertebrates, each gill bar is supported by a single cartilaginous rod
Horns and Antlers
- Hair horns are entirely composed of keratinized hair-like epidermal fibers, located on a roughened area of the nasal bone
- Antlers are characteristic of the deer family, formed by branched dermal bones, and are shed and replaced annually
Skeletal System
- Divided into axial skeleton (notochord, vertebral column, ribs, sternum, skull, and visceral skeleton) and appendicular skeleton (pectoral and pelvic girdles, skeleton of paired fins and limbs, and skeleton of median fins of fishes)
- Components of the head skeleton include chondrocranium, visceral skeleton, and dermatocranium
Chondrocranium and its Derivatives
- Supports the brain and organs of special sense (olfactory organs, eye, internal ears)
- Composed of various elements, including the notochord, prechordal cartilage, and parachordal cartilages
- May remain cartilaginous or become bony, but is always present
Dermatocranium
- Completes the framework of the skull
- Always bony and usually present, but has been lost in several major vertebrate groups
- Components include roofing bones, dermal bones of the upper jaw, bones of the primary palate, and opercular bones
Dermatocranium Elements
- Roofing bones provide a protective shield over the brain and special sense organs
- Dermal bones of the upper jaw include nasals, frontals, parietals, and postparietals
- Bones of the primary palate include lacrimal, prefrontal, post-frontal, post-orbital, and infraorbital
- Opercular bones include intertemporal, supratemporal, tabular, squamosal, and quadratojugal bones
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Description
This quiz covers the development of the chondrocranium and basal plate in vertebrates, including differences in formation and structure between species.
