ETHMOID BONE

Question 1

Ethmoid bone - OS ETHMOIDALE

Answer 1

• LIES deep within the skull
• LIES between the two orbits and the CAUDAL part of the Nasal cavity
• Resembles a horizontally placed tube
• The wall of the tube = LAMINA EXTERNA

Question 2

LAMINA EXTERNA Comprises

Answer 2

1. Lamina Tectoria -faces forehead
2. Lamina orbitalis
3. LAMINA BASALIS - forms the FLOOR

Question 3

Structures of the Ethmoid bone

Answer 3

1. LAMINA EXTERNA
   - lamina tectoria
   - lamina orbitalis
   - lamina basalis
2. LAMINA CRIBROSA
   - LIES transverselly
   - Separates nasal cavity from the Cranial cavity
   - Perforated Laminaa
   - Perforations allow passage of the OLFACtORy fibers (fila olfactoria) into the BULBUS olfactorius
3. LAMINA PERPENDICULARIS
   - a median Septum
   - Devides the nasal cavity into two
   - part of the Septum Nasi Osseum
   - FORMS THe CRISTA GALLI
4. LABIRINTHUS ETHMOIDALIS
   - Projects into interior of the bone from both the tectorial plate and the orbital lamina
   - Surrounds the coiled ETMOtURBINATES

-Ethmoturbinates
Project from the tectorial and orbital plates into the interior.

Each ETHMoTURBINaTE United to the outer Walls and behind to the cribriform plate by its basal plate
The basal lamellae project into the interior of the ethmoid - they form s spiral lamellae.
In ca: the Spiral lamellae have Longitudinal folds - give rise to secondary lamellar

Arranged in 2 rows (3 in eq)

• Endoturbinates
  The LARGER one!
  Extend far into the interior

- Ectoturbinates
Smaller ones
Remain externally
In EQ form a double row
In other species they are arranged
More lateral in position 
Can be seen from the interior once the Endoturbinates removed

of endo/ecto turbinates on each side:
Dog 4+6
Ru: 4-18
Eq: 6+25

• Endoturbinates I
  The most DORSAL
  The LARGEST
  Protrude forward into the nasal cavity beyond the wall of the ethmoid
• Attaches to the ethmoid Crest of nasal bone
• forms the bonybbase og the CONCHA nasalis dorsalis
• Endoturbinates II
• second in possition and size
• forms the basis of the CONCHA Nasalis Media
• MEATuS ethmoidalis
  LIES btw the ethmoturbinates