66 



BOXES OF TEE HEAD. 



The external ivcdl is the most extensive. The bones which take part 

 in its formation are the nasal, superior maxillary, ethmoid, inferior 

 spongy, and palate bones, and the internal pterygoid plates. The 

 superior and inferior turbinated pai'ts of the ethmoid bone (ethmo- 

 turbinal bone), and the inferior spongy bone (maxillo-turbinal), project- 



Fig. 55. — Vertical Antero- 

 posterior Section op a Part 

 OF THE Cranium, showing 

 THE Outer Wall of the Left 

 Nasal Fossa, &c. (A. T.) 4 



1, nasal bone ; 2, nasal i^ro- 

 cess of the suxaerior maxillaiy 

 Lone ; 3, ascending plate of the 

 jialate bone ; 4, superior turbi- 

 nated bone of the ethmoid — 

 Ijelow it the superior meatus, 

 behind it the opening into the 

 left sphenoidal sinus ; 5, the 

 middle turbinated bone — below 

 it the middle meatus, into which 

 opens the maxillary sinus ; superi- 

 orly and anteriorly, is the common 

 Oldening of the infundibulnm and 

 anterior ethmoidal cells ; behind 

 it, and above 3, the sjihcno- 

 palatine foramen ; 6, the inferior 

 turbinated bone — below it the 

 below these marks the section of the palatine plates of the left 

 palate and superior maxillary bones ; 7, the left frontal sinus ; 8, the left sphenoidal 

 sinus ; 9, the left optic foramen in the root of the lesser wing of the sphenoid, and 

 anterior cliuoid pi'ocess ; 10, the ridge of the dorsum sella3 divided ; and between 9 and 

 10, the sella turcica ; 11, the posterior surface of the petrous bone, close to the 

 internal auditory meatus ; 12, the b.asilar process of the occipital bone, close to the 

 foramen lacerum ijosterius ; 13, below the anterior condyloid foramen ; 14, left styloid 

 process ; 15, external, and 16, internal pterygoid processes ; 17, posterior palatine canal 

 and grooves. 



inferior meatus x x 



ing inwards, overhang the three divisions of the nasal fossas, called 

 meatus. The superior meatus, very short, is placed between the superior 

 and inferior turbinated parts of the ethmoid bone ; into it open anteriorly 

 the posterior ethmoidal cells, and posteriorly the spheno-palatine fora- 

 men and sphenoidal sinus. The middle meeitus, the space between the 

 inferior turbinated part of the ethmoid and the inferior spongy bone, 

 communicates at its fore part by means of the infandibulura, with the 

 anterior ethmoidal cells, and with the ft'ontal sinus, while in its middle is 

 the opening of the maxillary sinus. The inferior meatus, longer than 

 the others, lies between the inferior spongy bone and the floor of the 

 nasal cavity ; in its fore part is the orifice of the nasal duct and the 

 anterior palatine canal. 



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 early youth. The maxillary sinus begins to be 

 formed about the fourth month of foetal life ; the frontal, ethmoidal, and 

 sphenoidal first appear during childhood, 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 



