Skull and Hyoid 237 



It is clear, therefore, that the inner wall of the fossa is made by that part of the 

 vertical plate that lies below the foramen and which forms the sphenoidal process 

 behind this. The foramen is closed above by the body and turbinate of the sphenoid 

 and thus opens into the nasal fossa immediately below the roof, which is formed here 

 by the under surface of the sphenoid : in this way it becomes possible for nerves and 

 vessels passing through the foramen to turn down on the outer wall or to cross below 

 the roof and reach the septum, and thus to supply both sides of the nasal cavity. 



The extreme inner part only of the back of the maxilla forms the front wall of 

 the fossa ; the remainder makes the front wall of the zygomatic fossa, and the con- 

 tinuity of the two fossae is very clear on this bone. The upper margin of the bone 

 is the lower edge of the spheno-maxillary fissure, which opens from the orbit into the 

 two fossae : the extent to which the fissure opens into the spheno-maxillary fossa 

 is really determined by the size of the spheno-maxillary area on the great wing, as can 

 be seen on comparison of different skulls, so varies with the depth of the fossa. The 

 fissure is directed downwards and outwards, and thus the maxillary nerve reaches 

 its level by running outwards as well as forwards, without an upward direction : when 

 the fossa is shallow the nerve may pass from the spheno-maxillary into the zygomatic 

 fossa before reaching the level of the fissure. 



The direction and construction of the posterior palatine canal can be understood 

 by articulating the palate and maxilla, and the* situation and relations of the tuberosity 

 of the palate should be thoroughly investigated at the same time. 



To sum up : The fossa is connected with the cranial cavity by the foramen rotun- 

 dum, with the region of the naso-pharynx and Eustachian tube (see p. 225) by the Vidian 

 and pterygo-palatine canals, with the nasal fossa by the spheno-palatine foramen, with 

 the mouth cavity by the posterior palatine canal (from which minute foramina also reach 

 the outer wall of the nose), with the orbit by the spheno-maxillary fissure, and with the 

 zygomatic fossa through the pterygo-maxillary fissure. 



The structures passing through the spheno-maxillary fissure are : 

 Infraorbital nerve and vessels ; 

 Temporo-malar nerve ; 



Branches from Meckel's ganglion ascending to the orbit ; 

 The inferior ophthalmic vein. 



Passing through the pterygo-maxillary fissure are : 

 Internal maxillary vessels ; 

 Posterior dental nerves and vessels ; 

 Infraorbital nerve (sometimes). 



The spheno-maxillary fissure is closed externally by the malar, connecting the maxilla 

 and the sphenoid : rarely the maxilla may meet the sphenoid directly here, behind the 

 malar, and this is the only place where these two bones may come into contact. 



ETHMOID. 



This bone lies immediately below the ethmoidal notch in the frontal bone, which 

 is therefore closed by its upper surface, is applied to the front aspect of the sphenoidal 

 body, and rests below on and between the two maxillae. It thus forms the walls of 

 the upper portion of the nasal fossae. 



It consists of : (a) A median perpendicular plate which forms part of the bony 

 septum of the nose, articulating with the other elements of the septum, (b) An upper 

 horizontal cribriform plate, that is seen in the notch of the frontal, and is so named 

 because it is pierced by numerous foramina for the filaments of the olfactory nerves : 

 the inner edges of the orbital plates of the frontal rest on the horizontal top of the bone. 



