THE SKULL AS A WHOLE. 



part by the frontal and nasal bones, and the back part by the body of the sphenoid, 

 the ala of the vomer and the sphenoidal process of the palate bone. In it are the 

 apertures of the cribriform plate and the orifice of the sphenoidal sinus. 



The/oor, formed by the palate plates of the maxillary and palate bones, is smooth, 

 and concave from side to side. Towards its anterior extremity is the orifice of the 

 incisor foramen. 



The external wall is the most extensive. The bones which take part in its 

 formation are the nasal, superior maxillary, lachrymal, ethmoid, inferior spongy, and 

 palate bones, and the internal pterygoid plate. The superior and inferior turbinate 

 processes of the ethmoid bone, and the inferior spongy bone, projecting inwards, 

 overhang the three hollows called meatuses. The superior meatus, very short, 

 is placed between the superior and inferior turbinate parts of the ethmoid ; into it 



Fig. 73. SAGITTAL SECTION OF A PART OF THE 



SKULL, SHOWING THE OUTER WALL OF THE LEFT 



NASAL FOSSA, &c. (Allen Thomson. ) 



1, nasal bone ; 2, nasal process of the supe- 

 rior maxillary bone ; 3, vertical plate of the 

 palate bone ; 4, superior turbinate bone below 

 it the superior meatus, behind it the spheno- 

 ethmoidal recess and the opening into the left 

 sphenoidal sinus ; 5, middle turbinate bone 

 below it the middle meatus, into which opens 

 the maxillary sinus ; superiorly and anteriorly, 

 is the opening of the infundibulum ; behind it, 

 and above 3, the spheno-palatine foramen ; 

 6, inferior turbinate bone below it the inferior 

 meatus x x ; below these marks the section 

 of the palate plates of the left palate and supe- 

 rior maxillary bones ; 7, left frontal sinus ; 8, 

 left sphenoidal sinus ; 9, left optic foramen in 

 the root of the lesser wing of the sphenoid, and 

 anterior clinoid process ; 10, dorsum sellae di- 

 vided ; and between 9 and 10, the sella turcica ; 11, posterior surface of the petrous, close to the 

 internal auditory meatus ; 12, basilar process of the occipital bone, close to the jugular foramen ; 

 13, on the occipital condyle, below the anterior condylar foramen ; 14, styloid process ; 15. external, 

 and 16, internal pterygoid plates ; 17, posterior palatine canal. 



open anteriorly the posterior ethmoidal cells, and posteriorly the spheno-palatine 

 foramen. The middle meatus, the space between the inferior turbinate part of the 

 ethmoid and the inferior spongy bone, communicates with the anterior and middle 

 ethmoidal cells, with the maxillary sinus, and at its fore part, by means of the 

 infundibulum, with the frontal sinus. The inferior meatus, longer than the others, lies 

 between the inferior spongy bone and the floor of the nasal cavity, and in its fore 

 part is the orifice of the nasal duct. Above the superior meatus, in an angle 

 of the roof formed by the cribriform plate and the front of the body of the sphenoid 

 (fig. 73, behind 4), is a depression called the spheno-ethmoidal recess (Gr. H. Meyer), 

 formed by the narrowing of the lateral mass of the ethmoid (fig. 66) ; on Ihe 

 posterior wall of the recess is the opening of the sphenoidal sinus. 



The air-sinuses are hollows within the ethmoid, frontal, sphenoid, and maxillary 

 bones, which communicate with the nasal cavities by narrow orifices. With 

 the exception of the maxillary sinus these cavities are absent in the infantile skull. 

 The maxillary sinus begins to be formed about the fourth month of foetal life ; the 

 frontal, ethmoidal and sphenoidal first excavate the respective bones during child- 

 hood, but remain of small size up to the time of puberty, when they undergo a great 

 enlargement. In advanced life they all increase in size by absorption of the 

 cancellated tissue in their vicinity. The ethmoidal sinuses consist of several irregular 

 spaces occupying the lateral mass of the ethmoid, and completed by the frontal, 



