44 OSTEOLOGY. 



The Anterior end presents the perpendicular crista galli process, 

 in the median line, on each side of which are the ethmoidal fossse, 

 the cribriform lamellae of the ethmoid bone forming their anterior 

 boundary. 



NASAL FOSS^. 



The Nasal fossae are two cavities, separated in the fresh state 

 by a cartilaginous septum, which extends from the ethmoid bone 

 to the anterior nares. The framework of these fossae is formed 

 by the nasal, the superior maxillary, the frontal, and the palatine 

 bones, the whole forming a spacious irregular tube, bounded 

 posteriorly by the ethmoid bone, two turbinated bones being 

 situated in each fossa. The vomer in the median line, gives 

 attachment below to the cartilaginous septum. 



SIMUSES. 



These are winding cavities in the bones of the face. They 

 communicate freely with each otiier and with the nasal fossae, 

 of which they may be regarded as prolongations. Ordinarily, 

 they number four on each side — viz., the frontal, the maxillary, 

 the sphenoidal, and the ethmoidal. 



The Frontal sinus is situated inside the inner plate of the 

 orbital fossa, its extremely irregular walls being formed by the 

 frontal, nasal, lachrymal, ethmoid, and superior turbinated bones. 

 It communicates with the maxillary sinus belov/ by means of a 

 large opening through the delicate bony partition between them. 

 A thick vertical plate, often placed more to one side than the 

 other, and always imperforate, separates this sinus from that of 

 the opposite side. 



The Moixillary sinus, formed below, and before the orbit by 

 the superior maxillary, malar, ethmoid, lachrymal, and inferior 

 turbinated bones is the largest of the sinuses. A ridge which 

 contains the superior dental canal, divides it into tv/o chief 

 compartments — an internal, which is a shallow recess continuous 

 with the sphenoidal, and communicating with the ethmoidal sinus, 

 and an external, divided into two chambers by a transverse plate, 

 which frequently (according to some authorities, always) remains 

 perfect through life, and completely isolates the anterior chamber. 

 The posterior of these .chambers is prolonged backwards to the 

 alveolar tuberosity, and has the roots of the two last molar teeth 



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