THE ETHMOID 



83 



pieces of bone, the superior and middle nasal conchae (turbinate bones), and 

 encloses numerous irregularly shaped spaces, kno^vm as the ethmoidal cells. 

 These are arranged in three sets — anterior, middle, and posterior ethmoidal cells 

 ■ — and, in the recent state, are lined with prolongations of the nasal mucous 

 membrane. Laterally the labyrinth presents a thin, smooth, quadrilateral plate 

 of bone — the lamina papyracea (os planum) — which closes in the middle and 

 posterior ethmoidal cells and forms a large part of the medial wall of the orbit. 



By its anterior border it articulates with the lacrimal, and by its posterior border with the 

 sphenoid; the inferior border articulates with the medial margin of the orbital plate of the 

 maxilla and the orbital process of the palate bone, whilst the superior border articulates with 

 the horizontal plate of the frontal. Two notches in the superior border lead into grooves 

 running horizontally across the lateral mass to the cribriform plate, which complete, with the 

 frontal bone, the ethmoidal canals. The anterior canal transmits the anterior ethmoidal ves- 

 sels and (nasal) nerve; the posterior transmits the posterior ethmoidal vessels and nerve. 



Fig. 104. — Section through the Nasal Fossa to show the Labyrinth of the Ethmoid. 

 It shows also the lateral wall of the left nasal fossa. 



Superior nasal concha 

 Probe in sphenoidal foramen 



Sphenoidal sinus 

 Sella turcica 



Superior meatus 



Spheno-palatine 

 foramen 



Middle nasal 

 concha 



Uncinate process of ethmoid 



Medial pterygoid plate 



Palate bone 



Probe in posterior palatine canal 



Probe in naso- 

 lacrimal canal 



Frontal sinus 



Bristle in the 

 infundibulum 



Nasal bone 



Agger nasi 



Lacrimal bone 

 Lower end of bristle 

 in middle meatus 

 Middle meatus 



Inferior nasal 



concha 

 Probe at lower end 



of naso-Iacrimal. 



canal where it 



opens into inferior 



meatus 

 Incisive canal 



At the lower part of the lateral surface is a deep groove, which belongs to 

 the middle meatus of the nose, and is bounded below by the thick curved margin 

 of the inferior nasal concha. Anteriorly the middle meatus receives the in- 

 fundibulum, a sinuous passage which descends from the frontal sinus through the 

 anterior part of the labyrinth. The anterior ethmoidal cells open into the lower 

 part of the infundibulum, and in this way communicate with the nose, whereas 

 the middle ethmoidal cells open chrectly into the middle or horizontal part of the 

 meatus. In front of the lamina papyracea are seen a few broken cells, which 

 extend under, and are completed by, the lacrimal bone and the frontal process 

 of the maxilla; from this part of the labyrinth an irregular lamina, known as the 

 uncinate process, projects downward and backward. The uncinate process 

 articulates with the ethmoidal process of the inferior nasal concha and forms a 

 small part of the medial wall of the maxillarj^ sinus. 



Medially the labyrinth takes part in the formation of the lateral wall of the 

 nasal fossa, and presents the superior and middle nasal conchae (turbinate 

 processes), continuous anteriorly, but separated behind by a space directed for- 

 ward from the posterior margin. This channel is the superior meatus of the nose 

 and communicates wdth the posterior ethmoidal cells. The conchae are covered 



