186 



OSTEOLOGY. 



Frontal sinus 



Crista galli of ethmoid 



Cribriform plate of ethmoid 

 Sphenoidal sinus 



l/f 



HL Fossa hypophyseos 



Dorsum sella? 



of sphenoid 



The sinus in the orbital process of the palate bone either communicates with the 

 sphenoidal sinus, or else assists in closing in some of the posterior ethmoidal cells. 

 Its communication with the nasal cavity is through one or other of these spaces. 



The maxillary sinus lies to the lateral side of the nasal cavity, occupying the 

 body of the maxilla. Its walls, which are relatively thin, are directed upwards to 

 the orbit, forwards to the face, backwards to the infra-temporal and pterygo-palatine 

 fossae, and medially to the nose. In the latter situation the perpendicular part 



of the palate bone, the un- 

 cinate process of the ethmoid, 

 the maxillary process of the 

 inferior concha, and a small 

 part of the lacrimal bone 

 assist in the formation of 

 the thin osseous partition 

 which separates it from the 

 nasal cavity. The floor corre- 

 sponds to the alveolar border 

 of the maxilla, and differs 

 from the other walls in being 

 stout and thick ; it is, how- 

 ever, deeply pitted inferiorly 

 by the alveoli for the teeth. 

 The sinus opens by a 

 narrow orifice in the floor 

 of the hiatus semilunaris 

 into the middle meatus. 

 Occasionally there are two 



Angular spine Openings. 



The frontal sinuses lie, 

 one on either side, between 

 the inner and outer tables of 

 the frontal bone over the root 

 of the nose, and extend 

 FIG. 174. THE NASAL SEPTUM AS SEEN FROM THE LEFT SIDE. laterallv under the SUPer- 

 The frontal, maxillary, and sphenoid bones are coloured red ; the nasal, ciliary arches. The parti- 

 vomer, and basi- occipital blue ; the perpendicular part of the ethmoid fjrvQ which SGDirates them 



is usually central, though it 

 communicates with the nose 

 through a passage called the infundibulum, which opens inferiorly into the 

 anterior part of the corresponding middle meatus, below the ethmoidal bulla and 

 continuous with the hiatus semilunaris. 



The fact should not be overlooked that the air-spaces within the temporal 

 bone, viz., the tympanic cavity and the mastoid air-cells, are brought into com- 

 munication with the naso-pharynx through the auditory tubes. Further details 

 regarding the air-sinuses and the mode of their growth will be found under the 

 description of the individual bones. 



Frontal Sections. 



The relations of many parts of the cranium are best displayed in a series of frontal 

 (coronal) sections. 



By sawing off a thin slice from the front of the lower part of the frontal bone 

 above, and carrying the section downwards through the medial wall of the orbit and 

 the frontal process of the maxilla, into the piriform aperture below, a number of important 

 relations are revealed (see Fig. 175). In the frontal region the extent and arrange- 

 ment of the frontal sinuses are displayed. The partition between the two sinuses, 

 be it noted, is usually complete and central in position, though it may occasionally be 

 perforated or oblique. The sinuses are hardly ever symmetrical, the right being 

 usually the smaller of the two. (Logan Turner, Edin. Med. Journ. 1898.) 



The infundibulum on either side, leading from the frontal sinus above to the middle 



Vomer of sphenoid 

 Lateral pterygoid lamina 



Hamulus of medial 

 pterygoid lamina 



Foramen incisivum 



and the horizontal part of the palate bone are left uncoloured. 



may be deflected to one or other side. Each 



