Ethmoid bone | Cranial bones | Veterinary Anatomy

Table of Contents

Ethmoid bone is a single bone situated in front of the presphenoid and has a cribriform plate, a perpendicular part and two lateral masses.

It is a sieve-like partition between the cranial and the nasal cavities.
Its cranial surface is divided by the ethmoidal crest (crista galli) into two halves.
Each half forms the deep ethmoidal fossa for the olfactory bulb. The plate is perforated by numerous small foramen for the passage of the olfactory nerve filaments and on either side is the ethmoidal foramen for the ethmoidal artery and nerve.
The convex nasal surface has the lateral masses attached to it.

It forms he postero-dorsal part of the septum nasi and is covered by a mucous membrane.
Its dorsal border joins the junction of the frontals.
Its ventral border is received into the groove of the vomer.
Its anterior border is continuous with the septal cartilage in life.

Each lateral mass is the posterior part of the nasal cavity above and behind the posterior nares.
The perpendicular plate separates the two masses.
Each has the shape of cone with the base attached to the nasal surface of the cribriform plates.Each is curved on its lateral face by a thin plate of bone; the lamina lateralis.
The ventral part of this lamina is seen in the pterygo-palatine fossa forming the dorsal margin of the sphenopalatine foramen.
The mass consists of delicate, scroll-like plates of bone termed ethmo-turbinates. They are attached to the lamina lateralis and are separated by narrow intervals termed ethmoidal meatuses, which communicate with the nasal cavity.
In the fresh state, the ethmo-turbinates are covered with mucous membrane.
The largest ethmo-turbinates is so extensive that it projects between the dorsal and central turbinates and is often called the middle or third turbinate bone.
The mucous membrane covering the ethmo-turbinates is part of the olfactory mucous membrane.

The ethmoid bone is highly developed.
The cribriform plate is extensive and the olfactory fossae are very deep.
The ethmoidal crest is little developed and often incomplete.
The perpendicular plate is long.
The lateral masses are greatly developed and project into the frontal sinus.
The lamina lateralis is extensive and forms the medial wall of the maxillary sinus.
Its ventral border joins the palatine process of the maxilla and horizontal part of the palatine.
A shelf-like plate extends inward from its lower part and connects with the similarly incurved part of the palatine bone and meets outcurving plates of vomer to form the lamina transversalis, which divides the olfactory fundus of the nasal cavity from the lower nasopharyngeal meatus.