Skull and Hyoid 251 



moid, the downturned maxillary process of the inferior turbinate, and the vertical plate of the 

 palate bone (see Fig. 194). Its opening, narrowed by the approximation of these bones, is a small 

 slit between the uncinate process, palate, and turbinate : occasionally there is a double opening, 

 the accessory ostium being usually placed below and behind the ordinary opening. The sinus 

 begins to grow as an out-pouching of the side wall of the nose during the third month, and is present 

 at birth as a small cavity (circ. 5 x 5 X 12 mm.) in the inner part of the upper jaw. This extends 

 out as far as the line of the infra-orbital nerve during the first year, so that the situation of this nerve 

 is indicated by a bony ridge in the roof of the cavity during and after the second year. The sinus 

 grows with the bone, fairly quickly, up to the 8th or gth year, and after this rather more slowly, 

 corresponding with the slower eruption of teeth now occurring : after the later years of puberty, 

 its form is only altered by the addition of a postero-inferior angle associated with the last molar 

 development. These three indefinite stages of its growth seem to be indicated in its floor, where 

 there are two ridges, as a rule, visible : one of these is in the premolar region, and the other in the 

 molar region. Other ridges seen in the cavity include the infra-orbital ridge and the crest running 

 downwards and forwards from this, containing the anterior and middle dental nerves. At birth 

 the sinus is, of course, some distance above the level of the nasal floor, but its floor reaches this level 

 about the eighth year, and after this usually lies below the nasal level to a small extent. As the 

 teeth fall out with age, the floor rises and comes a little above the level of the nasal floor. The floor 

 is closely related to the roots of the molars, and does not often reach teeth in front of the second 

 premolar : the canine may, however, be in the front wall of large sinuses, and abnormal cavities 

 may occasionally extend in front of this. A large posterior ethmoidal cell may project into the 

 back and upper part of the cavity, even giving in some cases the appearance of the existence of a 

 double sinus. 



MALAR. 



An irregular bone which forms the outer wall of the orbit, separating it from the 

 temporal fossa, and rests on the maxilla below, making the prominence of the cheek : 

 it sends a process backwards, articulating with the zygoma of the temporal to complete 

 the arch. It thus can be described as possessing orbital, temporal and facial surfaces 

 in addition to the articular areas. It can be considered as formed by the junction of 

 two plates at an angle of about 70 degrees : the inner plate is curved to make a con- 

 cave orbital surface ; the outer plate forms the facial prominence, and is prolonged 

 back to meet the zygoma. The angle between the plates forms part of the temporal 

 fossa above, but below and in front it rests on the maxilla. 



The orbital surface is concave and has an outer vertical and a lower horizontal 

 portion : the outer part completes the outer wall of the orbit and articulates above 

 with the frontal and postero-internally by a serrated edge with the sphenoid ; the pro- 

 jection of this posterior edge is sometimes described as the orbital process. A small 

 tubercle or process on the upper part of the orbital surface marks the attachment 

 of the fascial band that acts as a check to the over-action of the outer Rectus, which 

 is in relation with the surface. The horizontal portion forms part of the floor of the 

 orbit, resting on the maxilla, and extends inwards as the infraorbital or maxillary 

 process : it is in contact with the Inferior Oblique muscle, and the opening of the malar 

 canal, for the temporo-malar nerve, is between it and the outer part. The inner border 

 of the horizontal portion articulates with the maxilla, and is continuous with the inner 

 sphenoidal border of the vertical part, but between the two articular areas is a small 

 non-articular portion of the margin (X in Fig. 200) which closes the outer end of the 

 spheno-maxillary fissure. 



The facial surface is slightly convex, producing a malar prominence, owing to the 

 backward inclination of its lower and outer part ; along its front border it is covered 

 by the lip of the maxillary surface that receives the bone. The remainder of the 

 surface is covered by fibres of Orbicularis palpebrarum, and, deep to this, gives origin 

 to the two Zygomatici on the prominence. 



A foramen on this surface transmits the malar division of the temporo-malar nerve. 



