244 



Anatomy of Skeleton 



Development. 



From a centre in membrane showing toward the end of the second month on 

 the surface of the nasal capsule. The nasal nerve is separated from it by the cartilage, 

 which does not completely disappear until after birth. A small second centre is said 

 to form its inner part in cartilage, the notch in the lower edge marking the junction 

 between the two portions. 



NASAL FOSS.E. 



The structure of the lateral masses of the ethmoid can be understood best, perhaps, 

 by a short study of the nasal fossa, which can be undertaken now with advantage. 



The Septum (Fig. 193) is easy of comprehension : observe how the whole of its upper 

 part is made by the perpendicular plate of the ethmoid, how this rests below and behind 



carfc'Uqe 



aosferror 

 nan'}. 



FIG. 193. Nasal septum seen from the left side. The section is a little to 

 the left of the middle line, so that the composition of the bony roof and 

 floor is shown, and the anterior palatine canal is not opened up by it. 



on the vomer, and how it projects forward far beyond the level of the rest of the bone 

 to articulate with the nasal spine of the frontal and to carry the nasal bones in front 

 of this. The other bones that enter into the formation of the septum are the frontal 

 spine, resting on the vertical plate and the crest (not always apparent) made in front of 

 this by the meeting of the nasal bones ; the crest, made by the two palate bones and two 

 maxillce where they meet and support the vomer ; the rostrum of the sphenoid, fitting 

 in between the ethmoid and vomer for a little distance. The remaining part of the 

 septum is made by the septal cartilage, and on this lie the vomerine cartilage (cartilage of 

 Jacobson) and the in-turned front part of the cartilage of the aperture. 



The structures concerned in the building of the outer wall, however, are not so 

 easily seen or understood. The student should endeavour first to obtain a clear idea 

 of what constitutes the absolute outer wall of the fossa, irrespective of the projections 

 and air cells that are attached to its nasal surface. Evidently the inner surface of the 



