THE ETHMOID BONE 



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are the smallest; they perforate the bone and transmit nerves to the roof of the 

 nose. At the front part of the cribriform plate, on each side of the crista galli, is 

 a small fissure, which transmits the nasal branch of the ophthalmic nerve; and 

 at its posterior part a triangular notch, which receives the ethmoidal spine of the 

 sphenoid. 



"Lamina cribrosa 



Crista galli 



Lateral mass 



Superior turbinated 



process 

 Superior meatus 



Processus uncinatus 



Inferior turbinated process 

 Perpendicular plate 



FIG. 63. Ethmoid bone from behind. 



Posterior 

 ethmoidal 

 foramen 



Anterior 

 ethmoidal 

 foramen 



Crista galli 

 Alar process 



FIG. 64. Ethmoid bone from above. (Spalteholz.) 



with 



The Vertical Plate (lamina perpendicularis) (Fig. 65) is a thin, flattened, 

 lamella of bone, which descends from the under surface of the cribriform plate, 

 and assists in forming the septum of the nose. It is much thinner in the middle 

 than at the circumference, 

 and is generally deflected 

 a little to one side. Its 

 anterior border articulates 

 with the nasal spine of the 

 frontal bone and crest of 

 the nasal bones. Its pos- 

 terior border, divided into 

 two parts, articulates by 

 its upper half with the 

 sphenoidal crest of the 

 sphenoid, by its lower 

 half with the vomer. The 

 inferior border serves for 

 the attachment of the 

 triangular cartilage of the 

 nose. On each side of 

 the perpendicular plate 

 numerous grooves are seen, 



leading from the foramina on the cribriform plate; they lodge filaments of the 

 olfactory nerves. 



The Lateral Mass, or Labyrinth (labyrinthus ethmoidalis), of the ethmoid 

 consists of a number of thin-walled cellular cavities, the ethmoidal cells (cellulae 

 ethmoidales), interposed between two vertical plates of bone, the outer one of which 

 forms part of the orbit, and the inner one part of the outer wall of the nasal fossa 

 of the corresponding side. There are two lateral masses, one on each side. The 

 ethmoidal cells are not present at birth, but appear during the fifth year. In the 



7 



FIG. 65. Perpendicular plate of ethmoid (enlarged), shown by removing 

 the right lateral mass. 



