168 OSTEOLOGY. 
to this rule there are many exceptions. On looking into the posterior fossa the anterior 
condylic and jugular foramina and the internal auditory meatus are seen in line, sloping 
from below upwards. The internal auditory meatus lies in a vertical plane, passing 
through the basion. ‘The grooves for the middle meningeal artery and its branches are 
very obvious. ‘The anterior groove curves forwards and outwards, and reaching the inner 
surface of the pterion, passes towards the vertex at a variable distance behind and more 
or less parallel to the coronal suture. From this, grooves pass forwards across the suture 
to reach the frontal bone. Another groove curves upwards and backwards a little below 
the line of the parieto-squamosal suture. From this, an upwardly-directed branch 
radiates on the inner surface of the parietal bone, in the region of the parietal eminence, 
whilst a lower branch passes backwards some little distance above the lambdoid suture, 
and gives offsets which curve downwards and inwards over the inner, surface of the 
squamous portion of the occipital bone. 
Nasal Fossze.—In the section through the nasal fossa the structures which form 
itsiouter wall can now be studied. These are—the nasal bone; the nasal process of 
the superior maxilla; the lachrymal bone; the lateral mass of the ethmoid, compris- 
ing the superior and middle turbinated bones ; the vertical plate of the palate bone ; 
the inferior turbinated bone ; and the mesial surface of the internal pterygoid plate. 
The roof as seen in the section is formed by the nasal and frontal bones, the cribri- 
form plate of the ethmoid, the body of the sphenoid and the sphenoidal turbinals, 
the sphenoidal process of the palate and the ala of the vomer. The floor, which is 
nearly horizontal from before backwards, is formed by the palatal processes of the 
superior maxilla and palate bones. On sagittal section the nasal fossa appears 
somewhat triangular in shape with the angles cut off; the base corresponds to the 
floor; the anterior and posterior nares to the truncated anterior and posterior 
angles respectively ; the superior angle is cut off by the cribriform plate; whilst the 
sides correspond to the frontal and nasal bones anteriorly, and the sphenoidal 
turbinals, sphenoidal process of the palate, and the ala of the vomer posteriorly. 
The cavity is therefore deep towards its middle, but gradually becomes shallower in 
front and behind where the openings of the nares are situated. The opening of 
the anterior naris, which is of half-heart shape, is larger than that of the posterior 
naris, and is directed forwards and downwards; the opening of the posterior is 
of rhomboidal form, and slopes backwards and downwards. The inferior meatus is 
the channel which is overhung by the inferior turbinated bone, and its floor is 
formed by the side-to-side concavity of the upper surface of the hard palate. 
Opening into it above, under cover of the fore part of the inferior turbinated bone, 
is the canal for the nasal duct; whilst its floor is pierced in front near the middle 
line by the anterior palatine canal. The middle meatus is the hollow between the 
middle and inferior turbinated bones ; it slopes from above downwards and back- 
wards, and is overhung by the free curved edge of the middle turbinal, beneath 
which there is a passage called the infundibulum, leading upwards and forwards to 
open superiorly into the frontal sinus, as well as into some of the anterior ethmoidal 
cells. Under cover of the centre of the middle turbinated bone there is an irregular 
opening leading into the maxillary sinus or antrum of Highmore, and there 
are frequently independent openings for the middle and some of the anterior 
ethmoidal cells. The superior meatus, about half the length of the middle meatus, 
is placed between the superior and middle turbinated bones i in the back and upper 
part of the fossa; it receives the openings of the posterior ethmoidal cells. Near 
its posterior extremity the spheno-palatine foramen pierces its outer wall, and brings 
it in relation with the spheno-maxillary fossa. The sphenoidal sinus opens on the 
roof of the nose, above the level of the superior turbinated bone, into a depression 
ealled the epbeno: ethmoidal recess. 
Nasal Septum.—If the opposite half of the section in which the osseous nasal 
septum is retained be now studied, it will be seen to be formed by the crests of the 
superior maxillary and palate bones below, on which rests the vomer, the posterior 
border of which being free, forms the posterior edge of the nasal septum, which 
slopes obliquely upwards and backwards towards the under surface of the body of 
the sphenoid. Here the vomer articulates with the rostrum of the sphenoid. In 
front of this the vomer articulates with the perpendicular plate of the ethmoid, 
