240 



Anatomy of Skeleton 



superior meatus is between the two turbinals (see Fig. 194). Fig. 198 gives the appear- 

 ance presented by the bones on section in situ. For further details of this region, 

 see p. 2.) 4. 



The lower walls of the middle ethmoidal cells form the part of the lateral mass 

 that rests (Fig. 188) on the maxilla, and the middle turbinal is a direct continuation of 

 these walls, so that when the walls become deficient behind the attached border of the 

 middle turbinal obtains another articulation, with the palate bone, the vertical plate 

 of which is here between it and the maxilla. 



The ethmoid articulates with the sphenoid and its turbinals behind, the palates 

 below, maxilla below and also in front, lachrymals laterally in front, frontal above, 

 and above and in front centrally, the two nasals and the vomer with its perpendicular 

 plate, and the two inferior turbinals through its uncinate processes. 



Development. 



The nasal fossae are at first enclosed, with the exception of their lower regions, 

 by a cartilaginous capsule which is continuous over the roofs of the fossae with the 

 cartilaginous septum : cartilaginous supports grow from this into the turbinal masses 

 and map out the air cells in part. Ossification starts on the surface of this capsule, 

 just behind the lachrymal region, in the fifth month, and extends slowly into the cell 

 walls and turbinates of the lateral mass, so that at birth the mass is practically ossified. 

 The septum, however, is still cartilaginous, and the roof is fibrous, the cartilage having 

 disappeared here. A centre appears in the membrane on each side of the upper part 

 of the septal cartilage during the first year, and from this the bony plate is slowly 

 formed during the next four or five years ; the crista galli is made by an early extension 

 from these centres. The bony lateral mass in the meantime has extended its ossification 

 into the roof and this joins with the completed septum. 



rrtmTt.1 forming roof- 

 of 



LACHRYMAL. 



Small shell-like bones placed near the front part of the inner orbital wall. Each 

 > bone articulates by its posterior margin with the 



os planum of the ethmoid, by its front border 

 with the nasal process of the maxilla, rests 

 below on that bone, and reaches the frontal 

 above : its deep surface covers the antero-lateral 

 aspect of the lateral mass of the ethmoid where 

 the os planum is deficient, and forms outer walls, 

 here for the anterior ethmoidal cells and the 

 infundibulum and a small part of the wall of the 

 middle meatus, and a prolongation downwards, 

 of this surface, making the inner wall of the 

 nasal duct, meets and articulates with an upper 

 process of the inferior turbinate bone which 

 forms the lower end of this inner bony wall. This 

 downward process of the lachrymal also articu- 

 lates by its posterior part with the uncinate 

 process of the ethmoid, and to a very small 

 extent helps to close in the opening of the antrum of Highmore. 



The deep surface shows impressions for the cells that are walled in by it. 



FIG. 189. Orbital aspect of right lach- 

 rymal bone, with the adjoining bones 

 indicated by interrupted lines. A., 

 process downwards forming inner wall 

 of nasal duct and joining inferior 

 turbinate ; B., hamular process ; 

 C., lachrymal crest. 



