Ethmoid bone

 ( Bones Of The Head And Neck ) 

• two bones of the neurocranium—the frontal bone, and the Sphenoid bone (at the sphenoidal body and at the sphenoidal conchae).
• eleven bones of the viscerocranium—, two nasal bones, two maxillae, two lacrimals, two palatine bone, two inferior nasal conchae, and the vomer.

The labyrinths are first developed, ossific granu. At birth, the bone consists of the two labyrinths, which are small and ill-developed. During the first year after birth, the perpendicular plate and crista galli begin to ossify from a single center, and are joined to the labyrinths about the beginning of the second year.

The cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths.

The development of the ethmoidal cells begins during fetal life.

The porous fragile nature of the ethmoid bone makes it particularly susceptible to fractures. The ethmoid is usually fractured from an upward force to the nose. This could occur by hitting the dashboard in a car crash or landing on the ground after a fall. The ethmoid fracture can produce bone fragments that penetrate the cribriform plate. This trauma can lead to a leak of cerebrospinal fluid into the nasal cavity. These openings let opportunistic bacteria in the nasal cavity enter the sterile environment of the central nervous system (CNS). The CNS is usually protected by the blood–brain barrier, but holes in the cribriform plate let bacteria get through the barrier. The blood–brain barrier makes it extremely difficult to treat such infections, because only certain drugs can cross into the CNS.

An ethmoid fracture can also sever the olfactory nerve. This injury results in anosmia (loss of smell). A reduction in the ability to taste is also a side effect because it is based so heavily on smell. This injury is not fatal, but can be dangerous, as when a person fails to smell smoke, gas, or spoiled food. In fact, older people with anosmia were more than four times as likely to die in five years compared to those with a healthy sense of smell.

Image:Gray149.png|Ethmoid bone from above.
Image:Gray150.png|Perpendicular plate of ethmoid.
Image:Gray151.png|Ethmoid bone (view from behind).
Image:Gray152.png|Ethmoid bone from the right side.
Image:Gray188.png|Side view of the skull.