EVOLUTION OF VISCERAL ARCHES
(=PHARYNGEAL ARCHES)
, 3 parts of the skull
1. Neurocranium/Chondrocranium - includes
a) cranium or the brain box
b) sense organs
– forms base of the skull
– composed of cartilage
– replaced by bones in most cases
2. Splanchnocranium - includes visceral (=pharyngeal) arches that support and move the
gills and contribute to production of jaws in gnathostomes & support for tongue and gill
region. These are primarily cartilaginous but may get partly invested or replaced by
membrane bones.
3. Dermatocranium - formed of membranous or dermal bones attached to neurocranium
and splanchnocranium. These bones roof over the chondrocranium or meet on its lower
surface
Temporary gaps called ‘FONTANELLES’ are left at the angles of the dermal parietal
bones in the skull of a young vertebrate. These allow growth of the cranium.
, Visceral arches or Pharyngeal arches
• Visceral arches are pieces of cartilages or bones that support
the pharyngeal region of vertebrates and also help attach
the jaws with the skull.
• Develop partly from neural crest cells and from splanchnic
mesoderm
• Includes series of horse-shoe shaped 7 pairs of cartilagenous
arches
• Encircle and support the pharynx between gill clefts
• Arches unite/interconnect ventrally but remain free dorsally
(=PHARYNGEAL ARCHES)
, 3 parts of the skull
1. Neurocranium/Chondrocranium - includes
a) cranium or the brain box
b) sense organs
– forms base of the skull
– composed of cartilage
– replaced by bones in most cases
2. Splanchnocranium - includes visceral (=pharyngeal) arches that support and move the
gills and contribute to production of jaws in gnathostomes & support for tongue and gill
region. These are primarily cartilaginous but may get partly invested or replaced by
membrane bones.
3. Dermatocranium - formed of membranous or dermal bones attached to neurocranium
and splanchnocranium. These bones roof over the chondrocranium or meet on its lower
surface
Temporary gaps called ‘FONTANELLES’ are left at the angles of the dermal parietal
bones in the skull of a young vertebrate. These allow growth of the cranium.
, Visceral arches or Pharyngeal arches
• Visceral arches are pieces of cartilages or bones that support
the pharyngeal region of vertebrates and also help attach
the jaws with the skull.
• Develop partly from neural crest cells and from splanchnic
mesoderm
• Includes series of horse-shoe shaped 7 pairs of cartilagenous
arches
• Encircle and support the pharynx between gill clefts
• Arches unite/interconnect ventrally but remain free dorsally
