n6 PRACTICAL ANATOMY. 



or diploic plate of bone. They are lined by mucous membrane. Infection is 

 very liable to occur in these sinuses. The difference between the mucous mem- 

 brane of the sinuses and that of the mouth is this : the latter is more vascular, 

 more hardy, more resisting, both to infection and traumatic causes, on account 

 of its location being such that exposes it to friction. Structure being the 

 correlative of function, an increased blood-supply would logically account for the 

 superior hardihood and less vulnerable character of the mucous membrane of 

 the mouth, and all other regions where friction is a consideration inseparable 

 from the environment. 



Take special notice that 



1. The orifice of the Eustachian tube is on a direct line with the inferior 

 meatus. 



2. A fine straw or bristle can be passed through the infundibulum (Fig. 77) 

 of the frontal sinus, into the middle meatus. 



3. A straw can be passed through the nasal duct into the inferior meatus ; 

 by turning the inferior turbinated bone up, you can easily see the orifice for the 

 nasal duct. 



4. The inferior meatus is located between the floor of the nasal fossae and 

 the inferior turbinated bone, and receives the end of the nasal duct. (Fig. 77.) 



NA5AL PROCESS 



RIOQE FOR MIDDLE TUHBINAL 



ANTRUM - E.'^^F:' Hiy ' If y LACHRYMAL GROOVE 



RIDGE FOR INFERIOR TURBINAL 



POSTERIOR PALATINE GROOVE fijU , I hjiWSag)- NA SAL SPINE 



PALATINE PROCESS -Jftfefc.. ^lagffi -CREST 



. ANTERIOR PALATINE GROOVE 



FIG. 78. THE LKFT MAXILLA. (Inner view.) 



5. The middle meatus is situated between the inferior and middle turbi- 

 nated bones. It receives the opening for the antrum, frontal sinus, and anterior 

 ethmoidal cells. (Fig. 77.) 



6. The superior meatus is located between the middle and superior turbi- 

 nated bones, and receives the openings for the sphenoidal sinus and for the 

 posterior ethmoidal cells. (Fig. 77.) 



The antrum of Highmore (maxillary sinus) (Figs. 68 and 76) occupies the 

 interior of the body of the superior maxilla. Its medical and surgical importance 

 entitle it to the following analytical consideration : 



1. It has a roof, a thin plate of bone that forms the floor of the orbit. In 

 this roof is the infraorbital nerve and vessels. (Fig. 51.) 



2. A floor formed by the alveolar process of the upper jaw. The fangs ot 

 the teeth may produce irregularities of this floor. (Fig. 76.) The surgeon may 

 gain access to the cavity by extracting a first or second molar tooth. 



3. Inner wall. The importance of this wall is the presence of the normal 

 opening, by which the antrum communicates with the nasal fossaj. (Fig. 77.) 

 The surgeon may gain access to the antrum for drainage by this wall. 



4. Anterior wall. On the inner surface of this wall are the anterior superior 



