for. It is probable that the nasal portion of the floor is often perforated in disease of the sinus.

Size of Cavity. The frontal sinuses vary much in size. They may be very large and extend outwards as far as the external angle of the orbit, upwards for one, two, or even two and a half inches, and backwards to the posterior part of the roof of the orbit. Turner gives as an average measurement : Height 31.6 mm., breadth 25.8 mm., and depth, measured along the roof of the orbit, 18 mm. The depth behind the supra-orbital margin is much

abnormally large and extends right across the middle line. The right frontal sinus is
a small cavity at the inner angle of the orbit.

less, averaging 4-8 mm. The frontal sinuses may be very small; they may be limited to small cavities situated at the internal angle of the orbit, the vertical portions being missing: occasionally both sinuses are entirely absent. The sinuses are frequently asymmetrical, a large cavity on one side being associated with a small one on the other: or only one cavity of a variable size may be found. A single large sinus may extend from one supra-orbital region to the other; the true nature of the cavity will be indicated by the presence of a single ostium communicating with only one nostril. Lothrop in two hundred and fifty specimens found both sinuses invariably present in the orbital region,

but in 3 per cent. the vertical portion was absent. He, however, describes one specimen with a large sinus on one side and apparently none on the other.1 Logan Turner, in two hundred and forty European skulls, found one or both sinuses absent in forty-one; that is in 17 per cent. Of these, in eighteen, that is in 7.5 per cent., both sinuses were absent, and in twenty-three, or 9.5 per cent., one sinus was absent. Tilley 2 found entire absence of the sinuses twice in 120 skulls, in one case in association with prominent brows. Kicer found both sinuses absent five times, and one sinus absent seven times in 195 skulls. Max Scheier 4 found no frontal sinus twice in 100 skulls. On the whole, the sinuses seem to be larger in males than in females, and are smaller and more often absent in races with receding foreheads; but the size of the cavity bears no constant relation to the prominence of the supra-orbital area.

In the living body two means may be adopted to ascertain the existence of sinuses-transillumination and the Röntgen rays. Of these the latter is the more reliable: when the sinuses are large their presence can be definitely determined, both by the screen and by photography, but if the sinuses are small, these means may fail. The results of transillumination are very uncertain. Unless a definite cavity can be demonstrated by means of the Röntgen rays, external operation alone can decide its presence or absence.

As in the antrum, bony and membranous ridges partially dividing the cavity are often found: they usually run in a vertical and antero-posterior direction. Very rarely there is a complete septum dividing a sinus into an inner and an outer part, but usually although it may appear complete, there is an opening at the lower part, so that both divisions of the sinus open into the nose through one ostium. Another condition simulating a double frontal sinus is the presence of a large ethmoidal cell extending well outwards over the orbit. One or two cells are normally present near the nasal floor of the sinus, and in rare specimens a cell as large as the frontal sinus itself may be found, and its true nature may be easily overlooked. Instances of true double frontal sinus are recorded by Scheier, Hansen, Pluder, etc., and I possess one specimen showing it on both sides.

The frontal sinuses may have various diverticula or recesses, especially near the outer angle, or there may be a prolongation from the inner end of the sinus into the crista Galli. According to Cryer, the latter is found. in 10 per cent. of specimens. These recesses are of considerable surgical importance, as they may be easily overlooked during operations: suppurating foci may be left behind and the operation may prove a failure.

1 Annals of Surg. 1898, xxviii. p. 622.

2 Lancet, 1896, ii. p. 867.

3

Laryngoscope, 1899, vi. p. 83.

Archiv für Laryngol., 1902, xii. p. 296, and Archiv Internat. de Laryngol., 1901, xiv. p. 321.

Development.

The frontal sinuses are absent at birth, and up till about the sixth year. They apparently begin to develop as a protrusion from the ethmoidal region at about the sixth or seventh year, and slowly spreading between the tables of the frontal bone, attain their full size and dimensions at or about the age of puberty. From nine to twelve years old fair-sized cavities have been seen (Symington). 1

Relations. The most important of the external relations of the frontal sinuses are as follows: The outer part of the inferior wall forms the roof of the orbit, and at its inner end is a small depression in which is fixed the pulley of the superior oblique muscle. The attachment of this pulley is often necessarily displaced in operations on the sinus.

margin is crossed at its inner end by the supra-trochlear vessels and nerve, which are necessarily divided in operations, but are of no great importance.

FIG. 13.-A DISSECTION SHOWING THE EXTERNAL RELATIONS OF THE FRONTAL SINUS. The right frontal sinus and infundibulum have been opened from the front. On the left side a skin flap has been turned back to show the position of the pulley of the superior oblique. a. Lachrymal duct; b. commencement of the infundibulum; c. nasal septum; d. pulley of the superior oblique; e. cavity of the frontal sinus; f line of incision in the supra-orbital margin; g. tendon of the superior oblique.

If the sinus extends far outwards the supra-orbital vessels and nerve also come into relation with its anterior wall (see Fig. 13).

The posterior wall is in relation with the dura mater and frontal lobe of the brain for the greater part of its extent, and with the olfactory lobe at its inner border.

The ostium of the frontal sinus is in the posterior part of the nasal portion of the floor, near the septum; being placed at the most dependent part of the cavity, it is well situated for drainage. It is round or oval, averaging 3 mm. in diameter, but varying from 2-8 mm. It leads into the infundibulum, a long curved canal (15 nim.) running downwards and backwards to the anterior end of the hiatus semilunaris This canal is convex forwards and downwards; it is bounded below by the uncinate process and the bulla ethmoidalis, and above by the anterior ethmoidal cells and the lachrymal bone. The canal may be wide and nearly straight, or

B

tortuous and narrow; its upper end is generally somewhat dilated. This is the commonly described arrangement, but very frequently (according to Lothrop in 50 per cent. of skulls), the frontal sinus opens directly through a short straight canal into the uppermost part of the middle meatus, and not into the hiatus semilunaris at all. In this case the infundibular canal terminates in an anterior ethmoidal cell (see Fig. 14). Some authors, e.g. Logan Turner, define the infundibulum as the cavity lying between the uncinate process and the bulla ethmoidalis, in which case the hiatus semilunaris means only the narrow slit-like entrance to this cavity. The upper closed-in part of the duct leading to the frontal sinus, which I have designated the infundibulum, is called by Turner the naso-frontal canal. The terminology I have adopted is the older, and there seems no good reason for altering it.

These considerations show the great difficulty of catheterizing the frontal sinus from the nose, a problem which has been much debated. Jurasz succeeded in introducing a probe eleven times in twenty-one cases, six times after considerable difficulty. Hansberg introduced a special very fine probe, bent at an angle of 135° about 30 mm. from its distal end; with this he claimed to enter about half the sinuses on the cadaver. Winckler 2 was successful in about one-fifth of his cases. Max Scheier was successful five times in thirty skulls, controlling his observations with the Röntgen rays. Zuckerkandl, after numerous experiments, concluded that the proceeding was attended with great difficulty and uncertainty, and the majority of observers agree with this opinion. On the other hand, Lichtwitz succeeded in entering ten out of thirteen sinuses on the cadaver, using a probe bent at a right angle about one inch from the end. Kicer 4 passed a probe successfully in 48 per cent. of 195 skulls. Lothrop, in an examination of 250 skulls with reference to this point, found that he could pass a probe into the sinus in about 25 per cent. Where a long infundibular canal led from the ostium frontale to the hiatus semilunaris probing was always impossible. Only when the infundibulum was a short, straight canal opening directly into the middle meatus, could probing be carried

out.

In 25 skulls in which the nose was opened by antero-posterior section, I found it possible to reach the sinus with a probe in only 6. Glätzel,5 controlling his observations by means of the X-rays, came to the conclusion that in many apparently successful results on the living, the probe was actually lying in an ethmoidal cell.

The chief obstructions to the passage of the probe arise from: 1. The middle turbinate, which entirely conceals the approach to the infundibulum. Before making an attempt to probe the frontal sinus, the anterior end of

1 Monatschr. für Ohrenheilk., 1890, xxiv. pp. 3, 43.

2 Archiv für Laryngol., 1894, i. p. 178. Laryngoscope, 1899, vi. p. 85.

3 Journal of Laryngology, xiii. p. 201.

Archiv für Laryngol., 1900, xi. p. 155.

this body should therefore be removed. 2. The uncinate process. When this process is prominent, and the infundibulum opens into the upper part of the hiatus semilunaris, probing is obviously impossible until it has also been removed. 3. The bulla ethmoidalis. When large it may encroach upon and considerably narrow the hiatus semilunaris. 4. The small calibre

FIG. 14-ANTERO-POSTERIOR SECTION THROUGH THE NOSF. Showing the frontal sinus opening into the middle meatus instead of into the infundibulum. 1, Infundibulum, which terminates in an ethmoidal cell; 2, probe in nasal duct, part of the inferior turbinate having been cut away; 3, frontal sinus showing probe in the duct leading into the middle meatus; 4, middle turbinate; 5, inferior turbinate.

or tortuous curve of the infundibulum. 5. The ostia of the ethmoidal cells, into which the probe is very liable to pass. As these usually open into the outer side of the infundibulum, they may be avoided by keeping the point of the probe close to the median line; but even then an occasional median ethmoidal cell may exist, the ostium of which can hardly be avoided.

During life the existence of these obstructions can never be certainly