FORM OF ROOF OF MOUTH.

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osseous septum of the nose be removed or destroyed during adult or old age, it leads to no perceptible change or external disfigurement. But if, on the contrary, such a casualty befall an individual during the period of childhood or youth, or before the development of the nasal organ has been fully accomplished, the nasal bones remain imperfectly advanced, and the nose presents a flattened or deformed appearance.

Many years ago, when visiting the cathedral at Gloucester, I was powerfully struck with the similarity displayed by a portion of its structure, to the position of the vomer in the nasal cavities. In one portion of this ancient cathedral there is an arch, and over it a second, that seems to derive its principal support from a vertical column placed between the two. Now, this is looked upon as an exceedingly elegant and beautiful piece of architecture, but it is only precisely similar to what every one carries about with him in his own nose the vomer and central lamella of the ethmoid forming the vertical column between the lower arch, or hard palate; and the upper arch, or nose and cribriform plate of the ethmoid.

The vomer at its inferior border is connected with the line of union, between the horizontal or palate plates of the superior maxillary bones. The expansion of the body of the sphenoid, therefore, into the sphenoidal cells, in advancing this bone downwards and forwards, has a tendency to press down the centre of the roof of the mouth, and thus to keep it rounded like a Norman arch, in order that it may correspond with the upper surface of the tongue. If the hard palate were allowed to assume an angular form, like that, in fact, of the Gothic arch; there would be an imperfect enunciation of certain letters on the part of the individual,

unless this deviation were rectified, by the introduction of an artificial roof or ceiling, susceptible of co-aptation to the rounded or convex surface of the tongue. Indeed, whilst mentioning this fact at lecture a few years since, a pupil afterwards came to me and said that there were certain letters that he was incapable of perfectly enunciating. On examining his mouth, I found the roof presented an angular or Gothic character; and on supplying an artificial and properly arched ceiling, his defective enunciation was quickly remedied.

The orbit constitutes a deep recess, on each side of the face, the walls of which are formed, not by a single or special orbital bone, but by the union or co-aptation of portions of the superior maxillary, malar, frontal, lachrymal, ethmoid, palate, and sphenoid. The bones of the cranium and face, that thus contribute to the formation of the orbit, are exceedingly numerous, compared with its extent; and this is a point that deserves attention, for I have no doubt, that it constitutes a special arrangement adapted with reference to some wise intention or design.

In such a region as the face, where such important sentient organs are contained in so small a space, it is necessary that the most perfect relation should be established between the growth and development of the several parts, in order to accomplish that beautiful harmony of the whole, that we meet with, as presented by Nature. Hence, therefore, instead of the organ of vision being placed in a cavity formed by a single bone, developed wholly in reference to this one consideration; it is placed in a recess encompassed by several bones, which, whilst they contribute by a portion of their surface to the formation of the orbit, are principally developed in

OBJECT OF PALATE BONE IN ORBITAL FLOOR. 89

relation to other purposes, connected with the functions of neighbouring parts. The orbit, indeed, is rather a recess intentionally hollowed out from the surrounding bones, and adapted for the reception of the optic apparatus, than a cavity primarily developed in relation to this sole object, without reference to the neighbouring structures. Again, the number of bones that enter into the formation of the orbit, would enable it to undergo a rapid growth or extension, each bone growing or enlarging around its own centre. And, if the orbit were formed of only one bone, provided with only a few centres of growth or extension; its enlargement might not be rapid enough, to correspond with the increasing perfection of the other parts belonging to the organ of vision.

Amongst the bones enumerated as assisting to form the parietes of the orbit, there is a small portion of the palate bone, that just shows itself at the extreme posterior part of the orbital floor. I have already alluded to the part that the development of the palate bone plays, in relation to the hard palate; and its orbital portion seems to be inserted in the orbit to carry out a precisely similar intention, namely, to fill up the gap or vacant space that would be otherwise occasioned by the advance of the ethmoid away from the body of the sphenoid, by the growth of the ethmoidal process of this bone. This is the only reason I can assign, for the constant entrance of this small process of the palate bone, into the construction of the walls of the orbit.

The orbit does not always remain of the same shape or configuration, for there is a most marked alteration of form or outline taking place during the earlier periods of life, or until the attainment of adult age. In the

infantile cranium, for example, the orbit presents a somewhat rounded outline or margin; in that of youth it is nearly oval; whilst in that of the adult it is more or less of a quadrilateral form. Another important change, also, that may be noticed, is, that in the adult the external angular process of the os frontis occupies a much more advanced and prominent position than in the youth or child,—a condition that is evidently intended to give increased space for the full development of the lachrymal gland, and likewise to afford greater security to the organ of vision, from accidental injury or external violence.

It is an extremely interesting fact, that all these changes in the form and outline of the orbit, are brought about through the influence of the growth and development of the sphenoid. So that, whilst one portion of the sphenoid is advancing the facial bones anteriorly; whilst another is altering the inclination of the petrous bones, and carrying the condyloid cavities further back, to give space for the molar teeth; the alæ majores are spreading out, and expanding or widening the whole of the upper parts of the face, and producing the alterations in the form of the orbits that I have just been alluding to.

The malar bone, which forms the principal portion of the outer wall of the orbit, rests upon the malar process of the superior maxillary bone. Now, this process, in growing outwards and backwards, necessarily carries with it the malar bone. And thus not only are the temporal and pterygoid fossæ deepened, for the full development of the muscles of mastication; but the semilunar edge of the malar bone that forms the outer margin of the orbit, being carried backwards,

CHANGES IN LOWER JAW.

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increases the extent or range of vision in a lateral direction.

If any one may choose to submit himself to the following observation, he will find that, if he place himself in the erect position and merely employ his cervical group of muscles, he will be able to turn his head on each side, so as to obtain a view of the whole circle, of which he himself forms the centre. But if, now, a small piece of paper be placed at the outer edge of the orbit, so as to advance, as it were, the outer wall, he will at once perceive that, had not the outer semilunar margin been kept back, the extent of lateral vision would have been considerably abridged, and that he would have been unable to have obtained a view of the whole circle around him, merely by the aid of the movements enjoyed by the head and neck.

The retroversion that takes place in the condition of the lower jaw with the arrival of old age, is exceedingly striking and remarkable, when viewed in relation to the other changes, that are at the same time approximating the condition of the old man to that of the child. If we follow, as has been done in the drawings at Plate IX., the form of the lower jaw through the different periods of life, we cannot but notice the similarity that exists between those belonging to the two extremes of age, and the difference that is observable between these, and those belonging to adult life. In the child, the angle between the body and the ramus is exceedingly obtuse; but as life advances a gradual change takes place, so that in the adult a nearly complete right angle is obtained. After this period, and during the decline of life, the angle again progressively reverts to the original condition it presented in the child.