A Treatise on the Eye/Book 1/Chapter 1
BOOK I.
Of the Parts subservient to the Eye.
CHAP. I.
Of the Supercilia or Eye-brows.
Sect.
Pag.
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| 1. | The Eye a curious and useful Organ, | 1 |
| 2. | It is either external or internal, | 3 |
| 3. | The first of the external Parts, the Eye-brows, | 3 |
| 4. | Man alone provided with Eye-brows, and why, | 4 |
| 5. | The Cassowar has something analogous to Eye-brows, and why, | 4 |
| 6. | The Eye-brows are prominent, and why, | 5 |
| 7. | They are corrugated and depressed by a Muscle, | 5 |
| 8. | The Advantages of this Motion, | 6 |
| 9. | The Eye-brows pulled up by the Frontals, | 7 |
CHAP. I.
Of the Supercilia or Eye-brows.
Sect. 1. OF all the Parts of the Body, there is none whose Structure and Mechanism discovers more Art and Design, than this little Organ the Eye; all its Parts are so excellently well contrived, so elegantly formed, and nicely adjusted, that none can deny it to be an Organ as magnificent and curious as the Sense is useful and entertaining. By means of this Organ, we discover the Magnitude, Figure, Distance, Situation, Motion, Colour and Beauty of Bodies: Without it, as all the Animal World would be in perpetual Darkness, so it would labour under perpetual Inconveniencies, be exposed to perpetual Harms, and suffer perpetual Wants and Distresses: But now, by this admirable Sense, we are enabled to see and chuse wholesome, yea delicate Food, provide ourselves useful, yea gaudy Cloathing, and commodious Places for Habitation and Retreat: We can dispatch our Affairs with Alacrity and Pleasure, go here and there as our Occasions call us, and, by looking about us, can discern and shun the Precipices and Dangers which would destroy us; we can now, if need be, ransack the whole Globe, penetrate into the Bowels of the Earth, descend into the Bottom of the Deep, travel to the farthest Regions of the World, to acquire Wealth, to increase our Knowledge, or even only to please our Fancy, and satisfy our Curiosity. And those glorious Objects which fill the Heavens and the Earth, those admirable Works of Nature which every where surround us, and which would be as nothing to us without being feen, do, by means of this noble Organ, present their Glories to our View, and fill us with Admiration and Delight. In a word, without the Benefit of Light, the animated Part of this System would be but so many Puppets tost up and down by Chance and Fortune, without House or Habitation, and deprived of all the Pleasures and Conveniencies of Life. What a miserable State would it be, to be confined to perpetual Darkness, and never to behold the chearful Light? But I need not expatiate on the Usefulness and Praises of this Sense, which we receive the Benefit of every moment, and the Want, or any Defect of which we lament among our greatest Misfortunes. I shall therefore proceed to examine the beautiful Structure of the Eye, from which we receive so many Advantages.
§ 2. For our clearer Proceeding in this Matter, I shall divide this Organ, after the common Manner of Anatomists, into two Parts, viz. the Internal, which is the Globe or Body of the Eye itself, formed by the Tunica cornea and Sclerotica, and the Parts contained in them; and the External, which are those Parts about the Globe subservient to it, such as the Supercilia or Eye-brows, the Cilia or Eye-lashes, the Palpebræ or Eye-lids, the Glandula Lachrymalis or Innominata, the Caruncula and Puncta Lachrymalia, &c. All which we shall describe in Order, beginning with the External Parts. And first of the Supercilia or Eye-brows.
§ 3. The Eye-brows, as every Body knows, are nothing else, but some Hairs placed above the Eye, which serve to defend it from Light when too strong, and especially from Dust, Mots, and such other Corpuscles floating in the Air, as, by falling into the Eye, might hurt its tender Substance, or render it opaque and unfit for transmitting the Rays of Light.
§ 4. Amongst all Creatures, Man alone is provided with Eye-brows; because his Skin is smooth, and consequently would easily allow such Particles to slide alongst it as might hurt the Eye, did not Nature provide against that Misfortune, by placing above it that thick Wood of Hairs.
§ 5. It is for the same reason that the Cassowar, that strange Bird, which, next to the Ostrich, is the greatest of all we know, being commonly five foot and a half in length from the End of the Beak to the Extremity of the Talons, and which has not been spoken of by any of the Antients, nor so much as known in Europe, till the Year 1597, that the Hollanders brought one from India; I say, it is for the same reason, that this Bird is provided with a Row of black Hairs, like a Demicircle at the Top of the Eye, raised like an Eye-brow, because the Skin of its Head and Neck is smooth and without Feathers: But other Animals that have a rough plumaccous or hairy Skin, have no occasion for Eye-brows, because the Roughness of their Skin alone is sufficient to answer their End.
§ 6. It is to be, observed, that the Eye-brows do always bunch out considerably more than the Eye, because of some Fat which is under the Skin in that Place, and because of the Eminence of that Part of the frontal Bone which lies under them.
The frontal Bone has two considerable Eminencies, one above each Eye, formed by the Separation of the two Tables of the Skull, which leave Cavities betwixt them commonly called the Frontal Sinuses. It is upon these Eminencies that the Supercilia are placed, and therefore they bunch out considerably above the Eye, which enable them the better to guard and defend it.
§ 7. There is yet another Mechanism provided by Nature by which the Eye-brows are excellently well fitted for defending the Eye, and that is, a Muscle, which, by its Contraction, draws the Eye-brows obliquely downwards, and at the same time does corrugate them, and make them approach one another.
Volterus Coiter, in his Observationes Anatomicæ, is the first I find who has described this Muscle. It arises from the great Canthus of the Orbit, precisely where the Os Nast is joined to the anterior Apophyse of the Os frontis, from which Origin it goes obliquely upward, and terminates by a Tendon in the Skin about the Middle of the Eye-brows.
Some Anatomists (whose Opinion Cowper, in his Myotomia Reformata, seems inclined to favour) reckon these Muscles only two oblique Elongations of the Frontals; but to me it appears of no consequence, whether they be thought distinct Muscles, or only such Prolongations, provided that their Use be understood.
All Anatomists agree, that these Muscles serve for pulling the Eye-brows obliquely downward, and at the same time for corrugating them, and making them approach one another: Their Origin and Insertion, and the Direction of their Fibres, shew plainly that to be their Use; and therefore they are named Corrugatores vel Depressores Superciliorum.
§ 8. From the Action of these Mufcles pulling down and corrugating the Eye-brows, we receive a twofold Advantage: 1mo, The Eye is better defended against Dust, Mots, and such like external Injuries. Hence it is that every body, when walking abroad, or riding in a dusty Road, (as all of us have often done in Summer, when the Roads are dry); I say, every body in that Case pulls down his Eyebrows as much as possible, that he may the better cover his Eyes, and defend them against the Dust and Mots with which the Air is then filled. 2do, A second Advantage we reap from this Depression of our Eye-brows, is the breaking and intercepting the Rays of Light, when the visual Object is too luminous, or when the Eye is placed in too bright a Light. Hence.in such Cases we also pull down our Eye-brows, that the Eye may be the better able to bear the Light, a Part of which is now intercepted by the depressed Eye-brows forming a kind of Shade on the Eye; and when the Eye-brows are not sufficient for this End, as sometimes happens when the Light is very strong, we can assist them by applying our Hand to our Forehead, by which our Eyes are more effectually shaded, so as to enable us to bear the Light, which otherwise would dazzle and hurt our Eyes. But when there is no Danger to our Eyes, either from Dust or Light, we pull up our Eye-brows, that none of the Light may be stopt, but that all of it may fall upon our Eyes; by which the Sight or Field of Vision is enlarged, and all the Objects above the Axis of Vision are now seen: whereas, when the Eye-brows were depressed, those most remote from this Axis, being shaded by the Eye-brows, could not be perceived.
§ 9. The Muscles which pull up our Eye-brows are the Frontales; they arise by a thin broad fleshy Beginning, from the upper Part of the Os frontis, from whence descending, they are inserted into the Skin of the Eye-brows, which they must therefore pull upward, that none of the Light may be stopt by them.