THE NASAL CAVITIES AND OLFACTORY STRUCTURES. 25 



increase is necessary to support the palate, which grows rapidly 

 in size at puberty. Up to the fifth year the upper jaw has to 

 carry only ten milk teeth ; in the adult it has to carry sixteen 

 permanent teeth. To support these the face and palate grow 

 rapidly in size. The formation of the frontal sinus gives the 

 necessary increase in the area of the base of the skull for their 

 support. It should be remembered that the growth of the brain 

 and of the cranial cavity is comparatively slight after the fifth 

 year. 



Only the gorilla and chimpanzee show an arrangement of 

 frontal and ethmoidal sinuses comparable to that of man. 



Above the hiatus lies the bulla ethmoidalis, which is inflated 

 by, and commonly carries the opening of, the middle ethmoidal 

 cell (Fig. 19). The posterior ethmoidal sinus opens beneath the 

 superior turbinate process, and is developed from the superior 

 meatus. The ethmoidal sinuses are produced in the cartilage 

 of the ethmoidal or lateral nasal plate (Fig. 7). They inflate 

 the ossifying cartilaginous plate until it becomes a cellular mass, 

 thus increasing the breadth of the intra-orbital septum. The 

 .sphenoidal sinus (Fig. 19) is formed by the mucous membrane 

 growing into and expanding the sphenoidal turbinate bone, which 

 is a small, slightly ossified cartilage lying beneath the pre- 

 sphenoid at birth, and forming the uppermost (sixth) of the nasal 

 turbinate processes. Latterly the sinus grows into and expands 

 the pre-sphenoid and part of the basi-sphenoid, the sphenoidal 

 turbinate remaining as its anterior wall (Fig 19). The 

 •sphenoidal turbinate is a detached part of the ethmoidal (lateral 

 nasal) cartilage. 



It will thus be seen that all the nasal air sinuses are produced 

 primarily by a budding outwards of the nasal mucous membrane 

 into the cartilaginous basis of the lateral nasal processes. Disease 

 may readily spread to these sinuses from the nasal cavities. 

 By means of the sinuses the area of the face is increased to 

 support the adult palate bearing the permanent teeth. Most of 

 them open on the respiratory tract of the nasal cavity. They 

 are ventilated with every breath. They act also as resonance 

 •chambers. 



Vestigial Turbinates. — There is frequently to be seen in the 

 adult one, or even two, secondary meatuses above the superior ; 



