188 



OSTEOLOGY. 



behind the zygomatic process of the frontal bone above ; inferiorly it passes through 

 the alveolar process of the maxilla in the interval between the first and second molar 



teeth. The cranial, orbital, nasal, 



J and maxillary cavities are all ex- 



posed, together with the roof of 



the mouth. 



The anterior cranial fossa is 



deepest in its centre, where its 

 floor is formed by the cribriform 

 plate of the ethmoid ; this corre- 

 sponds to the level of the zygo- 

 matico-frontal suture laterally. 

 On either side the floor of the 

 fossa bulges upwards, owing to 

 the arching of the roof of the 

 orbit. Of the orbital walls, the 

 lateral is the thickest and stoutest ; 

 the superior, medial, and inferior 

 walls, which separate the orbit 

 from the cranial cavity, the eth- 

 moidal cells, and the maxillary 

 sinus, respectively, are all thin. 

 The cavity of the maxillary 

 sinus lying to the lateral side of 

 the nasal cavity is well seen. 

 Its roof, which separates it from 

 the orbital cavity, is thin and 

 traversed by the infraorbital 

 canal. Its medial wall, with 

 which the inferior concha articu- 

 lates, is very slender, and forms 

 the lateral walls of both the 

 middle and inferior meatuses of 

 the nose. Its lateral wall is 

 stouter where it arches up to 

 bracket the temporal process of 

 the zygomatic bone. Its floor, 

 which rests upon the superior 

 surface of the alveolar border of 

 the maxilla, sinks below the level 

 of the hard palate. The fangs 

 of the teeth sometimes project 

 into the floor of the cavity. 



The nasal cavities are narrow 

 above, where they lie between 

 the orbital cavities, from which 

 they are separated by the cells 

 within the labyrinth of the 

 ethmoid. The roof which cor- 

 responds to the cribriform plate 

 is narrow, and lies between the 



18. Alveolar process of maxilla. sep tum medially and the laby- 



19. Groove for posterior palatine . r , , ., -, . i 



rmth on either side. 



At the level of the orbital floor 

 the nasal cavities expand later- 

 ally, the middle meatus running 



16 



22 21 20 19 



FIG. 176. FRONTAL SECTION PASSING INFERIORITY THROUGH 

 THE INTERVAL BETWEEN THE FIRST AND SECOND MOLAR TEETH. 



The frontal and maxillary bones, where cut, are coloured blue ; 

 the ethmoid, inferior conchse, and zygomatic red ; the vonier yellow. 



1. Groove for sagittal sinus. 



2. Crest for attachment of falx 



cerebri. 



3. Crista galli of ethmoid. 



4. Cribriform plate of ethmoid. 



5. Perpendicular part of eth- 



moid, assisting in the forma- 

 tion of the nasal septum. 



6. Labyrinth of ethmoid con- 



sisting of the ethmoidal cells. 



7. Lamina pap yracea of ethmoid. 



8. Middle meatus of nose. 



9. Middle concha. 



10. Opening from middle meatus 



into maxillary sinus. 



11. Orbital surface of maxilla. 



12. Zygomatico-frontal suture. 



13. Infra- orbital groove. 



14. Maxillary sinus. 



15. Canal for the anterior alveolar 



nerve and vessels exposed. 



16. Inferior concha. 



17. Inferior meatus of nose. 



21. 



nerve and greater palatine 

 vessels. 



20. Palatine process of maxilla. 

 Maxillary crest forming part 



vlrtg m P a rt of nasa, longitudinally in the angle formed 

 septum. by the labyrinth of the ethmoid 



with the body of the maxilla, 

 overhung by the middle concha. This channel is seen to have the ethmoidal 

 cells superior to it, the orbital cavity above and to the lateral side, the maxillary sinus 

 laterally, whilst its floor is formed by the superior surface of the inferior concha. 



The inferior meatus, much more roomy, runs along under cover of the inferior 



