9S SPECIAL ANATOMY OF THE SKELETON 



disarticulated bone many of these cells appear to be broken; but when the bones are 

 articulated they are closed in at every part, except where they open into the nasal 

 fossae. The upper surface of each lateral mass presents a number of apparently 

 half-broken cellular spaces; these are closed in, when articulated, by the edges of 

 the ethmoidal notch of the frontal bone. Crossing this surface are two grooves 

 on each side, converted into canals by articulation with the frontal; they are the 

 anterior and posterior ethmoidal canals (canalis ethmoidale anterius and posterius}, 

 and open on the inner wall of the orbit. The posterior surface also presents large 

 irregular cellular cavities, which are closed in by articulation with the sphenoidal 

 turbinated processes and the orbital process of the palate. The cells at the anterior 

 surface are completed by the lacrimal bone and nasal process of the maxilla, and 



those below also by the maxilla. 

 The outer surface of each lateral mass 

 consists chiefly of a thin, smooth, 

 oblong plate of bone, called the os 

 planum (lamina papyraced); it forms 

 part of the inner wall of the orbit, 

 and articulates, above, with the orbital 

 plate of the frontal; below, with the 

 maxilla; in front, with the lacrimal; 

 and behind, with the sphenoid and 

 orbital process of the palate. In 

 front of the os planum are found the 



FIG. 66.-Ethmoid bone. Inner surface of right lateral anterior ethmoidal Cells, which are 



completed by the lacrimal bone and 

 the nasal process of the maxilla. 



From the inferior part of each lateral mass, immediately beneath the os 

 planum, there projects downward and backward an irregular hook-like lamina 

 of bone, called the unciform process (processus uncinatus}; it serves to close in 

 the upper part of the orifice of the antrum (Fig. 71), and articulates with the 

 ethmoidal process of the turbinated bone. It is often broken in disarticulating 

 the bones. 



The inner surface of each lateral mass forms part of the outer wall of the nasal 

 fossa of the corresponding side. It is formed of a thin lamella of bone, which 

 descends from the under surface of the cribriform plate, and terminates below in 

 a free, convoluted margin, the middle turbinated process (concha nasalis media}. 

 The whole of this surface is rough and marked above by numerous grooves, which 

 run nearly vertically downward from the cribriform plate; they lodge branches 

 of the olfactory nerve, which are distributed on the mucous membrane covering 

 the bone. The back part of this surface is subdivided by a narrow oblique fissure, 

 the superior meatus of the nose (meatus nasi superior}, bounded above by a thin, 

 curved plate of bone, the superior turbinated process (concha nasalis superior}. 

 By means of an orifice at the upper part of this fissure the posterior ethmoidal 

 cells open into the superior meatus. Below, and in front of the superior meatus, 

 is seen the convex surface of the middle turbinated process. It extends along the 

 whole length of the inner surface of each lateral mass; its lower margin is free and 

 thick, and its concavity, directed outward, assists in forming the middle meatus. 1 

 It is by a large orifice at the upper and front part of the middle meatus that the 

 anterior ethmoidal cells, and through them the frontal sinuses, communicate with 

 the nose by means of a funnel-shaped canal, the infundibulum (infundibulum 

 ethmoidale}. The cellular cavities of each lateral mass, thus walled in by the os 

 planum in the outer side and by the other bones already mentioned, are divided by 



1 In 9 per cent, of specimens examined, Lothrop found that the ethmoidal cells were completed by the middle 

 turbinated processes. 



