nasal bones form the bony structure roof of the nasal cavity.
nasal bones form the bony structure roof of the nasal cavity.
what bone forms the bony structure roof of the nasal cavity?
nasal bones
a thin sagittal crest, constructed from the elongate nasal bones, ran up the skull midline before stopping just above the eye in a slightly flattened bulge. although the complete shape and height of this structure is unknown in "irritator", these head crests were commonplace in spinosaurids, having possibly served a display function when the animal was alive. the preserved part of "irritator"s crest is deepest above the antorbital fenestra and lacks the vertical ridges seen in the crest of "spinosaurus". like others in its family, "irritator" possessed a long and bony structure on the roof of its mouth called a secondary palate, separating the oral from the nasal cavity. this is a feature observed in extant crocodilians, but absent in most theropod dinosaurs. also like its relatives, "irritator" had two additional openings on the skull roof (called the postnasal fenestrae) as well as long and only partially diverging (bony extensions connecting the braincase with the palate). the back of the lower jaw was deep, its rear upper surface consisting mainly of the large bone, which with the shallower bone below it. the , a sideways-facing opening in the lower jaw, was oval and comparatively large. the (tooth-bearing bone of the mandible) is unknown in "irritator", save for a possible remnant at the front of the surangular. "irritator challengeri"s holotype is unique in that it is one of the few non-avian (or non-bird) dinosaur fossils found with a preserved stapes.
irritator
at the end of the sixth week the nasal pits have deepened further and they fuse to make a large ectodermal nasal sac. this sac will be above and to the back of the intermaxillary process. leading into the seventh week, the nasal sac floor and posterior wall grow to form a thickened plate-like ectodermal structure called the nasal fin. the nasal fin separates the sac from the oral cavity. within the fin, vacuoles develop that fuse with the nasal sac. this enlarges the nasal sac and at the same time thins the fin to a membrane - the oronasal membrane that separates the nasal pits from the oral cavity. during the seventh week the oronasal membrane ruptures and disintegrates to form an opening - the single primitive choana.  the intermaxillary segment extends posteriorly to form the primary palate which makes up the floor of the nasal cavity. during the eighth and ninth weeks a pair of thin extensions form from the medial walls of the maxillary process. these extensions are called the palatine shelves that form the secondary palate. the secondary palate will endochondrally ossify to form the hard palate - the end-stage floor of the nasal cavity.  during this time ectoderm and mesoderm of the frontonasal process produce the midline septum. the septum grows down from the roof of the nasal cavity and fuses with the developing palates along the midline. the septum divides the nasal cavity into two nasal passages opening into the pharynx through the definitive choanae.
human nose