134 DISSECTION OF THE NASAL CAVITY. 



orbits. This space is divided into two parts nasal fossae by a vertical 

 partition. 



Each fossa is larger below than above ; and is flattened in form, so that 

 the measurement from before back or above down exceeds much that from 

 within out. It communicates with both the fcce and the pharynx by 

 apertures named nares, and has also apertures of communication with the 

 sinuses in the surrounding bones, viz., frontal, ethmoid, sphenoid, and 

 superior maxillary. The student has to examine in each fossa a roof and 

 floor, an inner and outer wall, and an anterior and posterior opening. 



The roof is somewhat arched, and is formed by the cribriform plate of 

 the ethmoid bone in the centre ; by the frontal and nasal bones, and the 

 cartilages in front ; and by the body of the sphenoid, the sphenoidal spongy 

 bone, and the os palati, at the posterior part. In the dried skull many 

 apertures exist in it ; most are in the ethmoid bone for the branches of the 

 olfactory nerve with vessels, and one for the nasal nerve and vessels ; in 

 the front of the body of the sphenoid is the opening of its sinus. 



The floor is slightly hollowed from side to side, and in it are the 

 palate and superior maxillary bones their palate processes. Near the 

 front in the dry skull is the incisor foramen leading to the anterior pala- 

 tine fossa. 



The inner boundary (septum nasi) is partly osseous and partly carti- 

 laginous. The osseous part is constructed by the vomer, by the perpen- 

 dicular plate of the ethmoid bone, and by those parts of the frontal and 

 nasal with which this last bone articulates. The irregular space in front 

 in the prepared skull is filled in the recent state by the triangular carti- 

 lage of the septum, which forms part of the partition between the nostrils, 

 and supports the cartilages of the anterior aperture. Fixed between the 

 vomer, the ethmoid plate, and the nasal bones, this cartilage rests ante- 

 riorly on the median ridge between the superior maxillae, and projects 

 even between the cartilages of each nostril. The septum nasi is commonly 

 bent to one side. 



The outer boundary has the greatest extent and the most irregular sur- 

 face. Six bones enter into its formation, and they come in the following 

 order from before backwards : the nasal and superior maxillary ; the small 

 os unguis with the lateral mass of the ethmoid bone ; and posteriorly the 

 ascending part of the palate bone, with the internal pterygoid plate of the 

 sphenoid bone : of these, the nasal, ungual, and ethmoidal reach only about 

 half way from the roof to floor, whilst the others extend the whole depth. 

 Altogether in front of the bones, the lateral cartilages may be said to con- 

 struct part of this boundary. 



On this wall are three convoluted osseous pieces, named spongy or tur- 

 binate bones, (fig. 31), which project into the cavity : the two upper (*) 

 arid ( 2 ), are processes of the ethmoid, but the lower one ( 3 ), is a separate 

 bone the inferior spongy. The spongy bones are confined to a certain 

 portion of the outer wall, and their extent would be limited by a line con- 

 tinued nearly vertically upwards to the roof of the cavity from both the 

 front and back of the hard palate. Between each turbinate bone and the 

 wall of the nose is a longitudinal hollow or meatus ; and into these hollows 

 the nasal duct and the sinuses of the surrounding bones open. 



The meatuses are the spaces arched over by the spongy bones ; and as 

 the bones are limited to a certain part of the outer wall, so are the spaces 

 beneath them. 



The upper one (fig. 31, 6 ) is the smallest and straightest of the three 



