THE SINUS MAXILLARIS 109 



after that age a ridge on the roof of the sinus, which distinctly 

 indicates the course of the nerve in its canal. The degree 

 of prominence which the ridge may assume varies greatly 

 in the different specimens (Figs. 25, 26, 42, and 52) . In the 

 vast majority of cases there is thus formed a complete 

 osseous canal for the nervus inf raorbitalis ; but in some few 

 instances its osseous structure is incomplete, so that the 

 mucosa of the sinus becomes a part of the immediate sup- 

 port for the nerve. 



The osseous framework of the medial wall of the sinus 

 maxillaris consists of the thin portion of the corpus maxillae 

 surrounding the hiatus maxillaris, and also of the laminae 

 from contiguous bones partially filling in the hiatus. The 

 laminae, which form the incomplete portion of the wall, are 

 the processus maxillaris and the processus ethmoidalis 

 conchse nasalis inferior, the pars perpendicularis ossis pala- 

 tina, the processus uncinatus ossis ethmoidalis, and the pos- 

 tero-inf erior portion of the os lacrimale (Fig. 56) . With the 

 mucosa intact, the interstices between these laminae are 

 bridged over, leaving normally the ostium maxillare as the 

 only opening between the sinus and the nasal cavity. The 

 wall thus covered by mucosa usually forms a rather smooth 

 surface (Figs. 28, 45, and 49), but in some cases distinct 

 ridges may be produced by irregularities in the underlying 

 bone (Fig. 30). 



The ostium maxillare is in the anterosuperior portion of 

 the medial wall of the sinus maxillaris (Figs. 39, 45, and 49), 

 and is the point of communication between the sinus and 

 the infundibulum ethmoidale (Figs. 26, 37, and 52). The 

 ostium varies from a narrow, slit-like opening to forms oblong 

 or ovoid in outline. The average diameters of the ostia, 



