i THE CRANIUM. Eval 
infundibulum. A bony septum, rarely incomplete, separates the two sinuses; it 
is usually mesial in position below, but it may deviate to one or other side above. 
The sinuses vary considerably in their size and shape, independently of the 
degree of development of the elabella and superciliary ridges. According to 
Logan Turner, the dimensions of an av erage-sized sinus are: height, 14 in., from 
the lower end of the fronto-maxillary suture vertically upwards; breadth, 1 in., 
from the mesial septum horizontally outwards; depth, { in., from the anterior wall 
backwards along the orbital roof. The sinus may exist merely as recesses limited 
to a small area of bone above the nose, or it may extend upws ards on to the fore- 
head for more than two inches; externally it may be limited by the bony 
wall of the temporal fossa, while posteriorly it may re ach as far back as the optic 
foramen. The anterior wail is thickest, but the thickness may vary from 1 to 
Rod leading from frontal sinus through 
infundibulum into middle meatus 
Section of eyeball a Cribriform Posterior part Lachrymal External angular 
little behind the cornea — Roof of orbit plate of frontal sinus gland process of frontal 
Crista | 
Galli 
Anterior 
~~ ethmoidal cell 
Anterior part of 
middle turbinal 
~~ Rod in lower part 
of nasal duct 
Rod leading from 
frontal sinus through 
infundibulum into 
middle meatus 
Septum nasi 
Anterior part of 
Opening of lower end antrum of Highimore 
of nasal duct into 
inferior meatus 
Rod leading from lower 
part of nasal duct into - 
inferior meatus 
_ Anterior extremity of 
inferior turbinal 
Fic. 798.—-VERTICGAL CORONAL SECTION THROUGH THE ANTERIOR PART OF THE ORBITAL AND 
NASAL CAVITIES AND THE UPPER LIP. 
5mm. The floor is the thinnest wall, hence when pus is retained within the 
cavity, it tends to point at the upper and inner angle of the orbit. Intracranial 
_ suppuration may arise in connexion with sinus disease by extension through the 
posterior wall. ‘The muco-periosteal lining, which readily strips from the hone, is 
| thin and pale, and provided with mucous-secreting glands. 
In many individuals, by the aid of trans-c/lumination, the extent of the sinuses and the 
position of the intervening septum may be mapped out upon the forehead. For this 
purpose a small electric lamp i is placed against the floor of the sinus, beneath the inner 
third of the supra-orbital margin. In exploring the sinus, the opening in the bone should 
_ be made close to the mesial plane, immediately above the root of the nose. In marked 
cases of deviation of the septum one sinus may extend so far across the mesial plane of 
the forehead as to reduce the other to a mere slit ; in such cases the surgeon may fail to 
open the diseased sinus when the operation is performed through the anterior wall. The 
sinus frequently contains incomplete partitions, which give rise to the formation of pockets 
_and recesses usually found towards the external angle of the sinus; when dealing with 
‘chronic suppuration of the sinuses, special attention ‘should be paid to these recesses as 
well as to the backward extension of the cavity along the orbital roof. The anterior 
