THE NASAL FOSS.E 79 



In old skulls the frontal sinuses occasionally extend into that ])ortion of the 

 horizontal plate of the frontal bone which forms the roof of the orbit. 



The following muscles arise within the orbit : — the four recti, the mperior 

 oblique, and levator palpebrx svperioris, near the apex; the inferior oblique on the 

 floor of the orbit external to the lachrymal canal; and the tensor tarsi from the 

 lachrymal crest. The margins of the s])heno-maxillary fissure give attachment to 

 the orbit alis muscle (see section on the Eye). 



The nasal fossae or sinuses are two irregular cavities situated on each side of 

 a median vertical septum, extending from the anterior part of the skull-base to the 

 superior surface of the hard palate. They are somewhat oblong in section, but are 

 narrower above than below. 



Each fossa presents a roof, floor, imier and outer wall, and opens in front Ijy 

 the anterior naris, and communicates behind with the pharynx Ijy the posterior 

 naris. 



The roof resembles that of a house with two sloping edges and an intermediate 

 level portion. The anterior slope is formed by the posterior surface of the nasal 

 bone and the nasal spine of the frontal. ■ The horizontal portion corresponds to the 

 cribriform plate of the ethmoid and the sphenoidal turbinal. The posterior slope 



Fig. 87. — Section through the Nasal Fossa to show the Septum. Left Half, with 

 Septum looking towards Right Nasal Fossa. 





CREST OF SPHENOID "^r J ' 'A^ ^^^Pf*^^^ * " ^^X ' NASAL SPINE OF FRONTAL 



GROOVE FOR NASAL NERVE iV^^jj^ ^-v.^ 



CREST OF PALATE BONE 



SPINE OF PALATE BONE - ^^- hit^Z^^ j;-^=,__i£"2= CREST OF MAXILLA 



is formed by the inferior surface of the body of the sphenoid, an ala of the vomer, 

 and a small portion of the sphenoidal process of each palate bone. The sphenoidal 

 sinus opens at the upper and back part of the roof into the spheno-ethmoidal recess 

 or superior meatus of the nose. 



The floor is wider than the roof, concave from side to side, and has a slight 

 backward slope. It is formed mainly by the palatine process of the maxilla, and 

 comj^leted posteriorly by the horizontal plate of the palate bone. Near its anterior 

 part, close beside the septum, is the anterior palatine canal. 



The septum, or inner wall, is formed by the crest of the sphenoid, the crest of 

 the nasal bones, nasal spine of frontal, the mesethmoid, vomer, and the median 

 crest formed by the apposition of the palatine plates of the maxillae and the hori- 

 zontal plates of the palate bones. The anterior border has a triangular outline, 

 limited above by the mesethmoid, and below by the vomer. This receives the 

 triangular cartilage of the nose. The posterior border is formed by the pharyngeal 

 edge of the vomer. The septum is usually deflected to one side, and is occasionally 

 perforated. Sometimes a stri]) of cartilage, continuous Avith the triangular cartilage, 

 persists between the vomer and mesethmoid. 



The outer wall is formed by tlie nasal process and inner wall of the maxilla, 

 the lachrymal, the ethmoidal and inferior turbinals, the vertical plate of the palate 



