FOOTNOTES:
[a] In Dissectionibus anatomicis vix aliquid admirabilius, aut artificiosius structurâ Oculi humani, meo quidem judicio, occurrit: ut meritò, per excellentiam, Creatoris appelletur Miraculum. Gul. Fabr. Hildan. Cent. 2. Observ. 1.
So likewise that accurate Surveyor of the Eye, Dr. Briggs, whose Ophthalmography I have met with since my penning this part of my Survey. His Character of this curious piece of God’s Work is, Inter præcipuas corporis animati partes, quæ magni Conditoris nostri sapientiam ostendunt, nulla sanè reperitur, quæ majori pompâ elucet quàm ipse Oculus, aut quæ elegantiori formâ concinnatur. Deum enim aliæ partes vel minori satellitio stipantur, vel in tantam venustatem haud assurgunt; Ocelli peculiarem honorem & decus à supremo Numine efflatum referunt, & nunquam non stupendæ suæ Potentia characteres repræsentant. Nulla sanè pars tam divino artificio & ordine, &c. Cap. 1. §. 1.
[] It is a good Reason Frier Bacon assigns for the Sphæricity of the Eye: Nam si esset planæ figuræ, species rei majoris oculo non posset cadere perpendiculariter super eum——Cùm ergò Oculus videt magna corpora, ut ferè quartam cœli uno aspectu, manifestum est, quòd non potest esse planæ figuræ, nec alicujus nisi sphæricæ, quoniam super sphæram parvam possunt cadere perpendiculares infinitæ, quæ à magno corpore veniunt, & tendunt in centrum Sphæræ: Et sic magnum corpus potest ab oculo parvo videri. For the Demonstration of which he hath given us a Figure. Rog. Bacon. Perspect. Distinct. 4. Cap. 4.
Dr. Briggs saith, Pars antica, (sive Cornea,) convexior est posticâ: hâc enim ratione radii meliùs in pupillam detorquentur, & Oculi fundus ex altarâ parte in majorem (propter imagines rerum ibidem delineandos) expanditur. Ibid. §. 2.
[c] Suppose the Eye had the Retina, or back part flat for the Reception of the Images, as in [Fig. 1.] ABA: it is manifest, that if the Extremes of the Image AA were at a due focal distance, the middle B would be too nigh the Crystalline, and consequently appear confused and dim; but all Parts of the Retina lying at a due focal distance from the Crystalline, as at ACA, therefore the Image painted thereon is seen distinct and clear. Thus in a dark Room, with a Lens at a Hole in the Window, (which Sturmius calls his Artificial Eye, in his Exercit. Acad. one of which he had made for his Pupils, to run any where on Wheels). In this Room, I say, if the Paper that receives the Images be too nigh, or too far off the Lens, the Image will be confused and dim; but in the Focus of the Glass, distinct, clear, and a pleasant Sight.
[d] Blemmyis traduntur capita abesse, Ore & Oculis pectori affixis. Plin. Nat. Hist. l. 5. c. 8. Occidentem versus quosdam sine cervice Oculos in humeris habentes. Ib. l. 7. c. 2. From these, and other such like Fables, in this last cited Chapter of Pliny, no doubt our famous Romancer Sir J. Mandevile, had his Romnantick Stories related in his Travels.
[e] See [Book V. Chap. 2. Note (e).]
[f] Galen deserves to be here consulted, who in his Book De Usu Partium, from many Considerations of the Hand, such as what is here mentioned, as also its Structure, Site and Use, largely proves and reflects upon the Wisdom and Providence of the Contriver and Maker of that Part.
[g] Thus in Hares and Conies, their Eyes are very protuberant, and placed so much towards the sides of their Head, that their two Eyes take in nearly a whole Sphere: Whereas in Dogs, (that pursue them) the Eyes are set more forward in the Head, to look that way more than backward.
[h] Sed lubricos Oculos fecit [Natura] & mobiles, ut & declinarent siquid noceret; & aspectum, quo vellent, facile converterent. Cicer. de Nat. Deor. l. 2. c. 57.
[] The Eyes of Spiders, (in some four, in some six, and in some eight) are placed all in the fore-front of their Head, (which is round, and without any Neck) all diaphanous and transparent, like a Locket of Diamonds, &c. neither wonder why Providence should be so anomalous in this Animal, more than in any other we know of. For, 1. Since they wanting a Neck, cannot move their Head, it is requisite that Defect should be supplied by the multiplicity of Eyes. 2. Since they were to live by catching so nimble a Prey as a Fly is, they ought to see her every way, and to take her per saltum, (as they do) without any Motion of the Head to discover her: Which Motion would have scared away so timorous an Insect. Power’s Micros. Observ. pag. 11.
The Eyes of the Cameleon resemble a Lens, or Convex Glass, set in a versatile globular Socket, which she turneth backward, or any way, without moving her Head; and ordinarily the one a contrary, or quite different way from the other. Dr. Goddard in Phil. Tran. Nᵒ. 137.
But what is more extraordinary in this Motion [of the Cameleon’s Eye] is to see one of the Eyes move, whilst the other remains immoveable; and the one to turn forward, at the same time that the other looketh behind; the one to look up to the Sky, when the other is fixed on the Ground. And these Motions to be so extreme, that they do carry the Pupilla under the Crest which makes the Eye-brow, and so far into the Canthi, or Corners of the Eyes, that the Sight can discern whatever is done just behind it, and directly before, without turning the Head, which is fastned to the Shoulders. Mem. for a Nat. Hist. in Anatom. Dissect. at Paris. Diss. of Camel. pag. 22.
[k] Snails send out their Eyes at a distance, they being contained in their four Horns, like atramentous Spots, fitted to the end of their Horns, or rather to the ends of those black Filaments or optick Nerves, which are sheathed in her Horns, as Dr. Power wordeth it. Obs. 31. pag. 36. So the ingenious Dr. Lister. Exercit. Anat. Cochl. & Limac.
[l] Vid. [l. 8. c. 3. Note (a).]
[m] Severinus is of Aristotle’s, Pliny’s, and Alb. Magnus’s Opinion, that the Mole hath no Sight; G. Seger denies any Humour to be therein, but thinks they may probably see, because Nature made nothing in vain. But Borrichius saith, their Eyes have appendiculam nerveam in cerebrum euntem, cujus beneficio globuli illi [the little Eyes] extra pellem facilè poterant exseri, retrahique pro arbitrio——In illis oculorum globulis humor aqueus copiose satis natabat; cæterorum non nisi tenue vestigiem. Blas. Anat. Anim. c. 35.
Et quoniam Natura hoc vitæ genus ipsi destinavit, etiam perquàm exiguos Oculos——dedit eo concilio, ut ii, pretiosissima corporis pars, à terræ pulvere nè affligerentur. Ii insuper pilis recti, &c. Humores illis oculis insunt, & tunica nigra, uvea, se prodit. Ad hos tramite alio nervus venit. Schneider in Blas. ibid.
Some time since I made divers accurate Dissections of the Eyes of Moles, with the help of Microscopes, having a doubt whether what we take to be Eyes, were such or no. And upon a strict Scrutiny I plainly could distinguish the Vitreous and Crystalline Humours, yea, the Ligamentum Ciliare, and the atramentaceous Mucus. The Pupil I could manifestly discern to be round, and the Cornea copped, or conical: The Eye is at a great distance from the Brain, the Optick Nerve very slender and long, reaching from the Eye through the intermediate Flesh, and so passeth to the Brain, along with the pair of Nerves reaching to the Nose, which are much the largest that are in all the Animal. These Creatures, I imagine, have the Faculty of withdrawing their Eyes, if not quite into the Head, (as Snails) yet more or less within the Hair, as they have more or less Occasion to use or guard their Eyes.
Galen saith, Moles have Eyes, the Crystalline and Vitreous Humours, encompassed with Tunicks. De Us. Part. l. 14. c. 6. So accurate an Anatomist was he for his Time.
[n] Pliny tells us of a sort of Heron with but one Eye, but ’twas only by hear-say. Inter Aves Ardeolarum genere, quos Leucos vocant, altero oculo carere tradunt. Nat. Hist. l. 11. c. 37. So the King of the Nigræ that hath but one Eye, and that in his Forehead, l. 6. c. 30. Which Fables I take notice of more for the Reader’s Diversion, than any Truth in them.
[o] Supra, [Note (i).]
[p] The most celebrated Anatomists differ greatly about the Reason why we see not double with two Eyes. This Galen, and others after him, generally thought to be from a Coalition or Decussation of the Optick Nerves, behind the Os Sphenoïdes. But whether they decussate, coalesce, or only touch one another, they do not well agree. The Bartholines expressly assert they are united, non per simplicem contactum vel intersectionem in homine, sed totalem substantiæ confusionem, Anat. l. 3. c. 2. And whereas Vesalius, and some others had found some Instances of their being disunited; they say, sed in plerisque ordinarie confunditur interior substantia, ut accuratâ disquisitione deprehendi.
But our Learned Dr. Gibson, (Anat. l. 3. c. 10.) saith, they are united by the closest Conjunction, but not Confusion of their Fibres.
But others think the Reason is not from any Coalescence, Contact, or crossing of the Optick Nerves, but from a Sympathy between them. Thus Monsieur Cartes is of Opinion, that the Fibrillæ constituting the medullary Part of those Nerves, being spread in the Retina of each Eye, have each of them corresponding Parts in the Brain; so that when any of those Fibrillæ are struck by any part of an Image, the corresponding Parts of the Brain are thereby affected, and the Soul thereby informed, &c. but see more hereafter under [Note (oo)], from Cartes himself.
Somewhat like this is the Notion of our judicious Dr. Briggs, who thinks the Optick Nerves of each Eye consist of Homologous Fibres, having their rise in the Thalamus Nervorum Opticorum, and thence continued to both the Retinæ, which are made of them; And farther, that those Fibrillæ have the same Parallelism, Tension, &c. in both Eyes; and consequently when an Image is painted on the same corresponding, sympathizing Parts of each Retina, the same Effects are produced, the same Notice or Information is carried to the Thalamus, and so imparted to the Soul, or judging Faculty. That there is such an Ὁμοιοπάθεια between the Retina, &c. he makes very probable from the ensuing of double Vision upon the Interruption of the Parallelism of the Eyes; as when one Eye is depressed with the Finger, or their Symphony interrupted by Disease, Drunkenness, &c. And lastly, That simple Vision is not made in the former way, viz. by a Decussation or Conjunction of the Optick Nerves, he proves, because those Nerves are but in few Subjects decussated, and in none conjoined otherwise than by a bare Contact, which is particularly manifest in Fishes; and in some Instances it hath been found, that they have been separated without any double Vision ensuing thereupon. Vid. Brig. Ophthalmogr. cap. 11. & 5. and Nov. Vis. Theor. passim.
What the Opinion of our justly eminent Sir Isaac Newton is, may be seen in his Opticks, Qu. 15. Are not the Species of Objects seen with both Eyes, united where the Optick Nerves meet before they come into the Brain, the Fibres on the right side of both Nerves uniting there, &c. For the Optick Nerves of such Animals as look the same way with both Eyes, (as of Men, Dogs, Sheep, Oxen, &c.) meet before they come into the Brain; but the Optick Nerves of such Animals as do not look the same way with both Eyes, (as of Fishes and of the Cameleon) do not meet, if I am rightly informed. Newt. Opt. Q. 15.
[q] Nigra est [Uvea] ut radios (ab Oculi fundo ad anteriorem ejus partem reflexos) obumbret; nè hi (ut ait clar. Cartesius) ad Oculi fundum retorti ibidem confusam visionem efficerent. Alia forsan ratio hujus nigredinis statuatur, quòd radii in visione superflui, qui ab objectis lateralibus proveniunt hoc ritu absorbeantur. Ita enim è loco obscuro interdiu objecta optimè intuemur, quia radii tunc temporis circumfuso lumine non diluuntur. Brigg’s Ophthal. c. 3. §. 5.
[r] Admirandum Dei artificium ex diversorum animalium comparatione indies evadit manifestiùs. Mirantur omnes Trochlearem in oculis Hominum & Quadrupedum, & quidem jure: sed admirationem omnem superat, quòd sine Trochleâ oculum movens in Avibus novum genus Trochleæ longè artificiosiùs Nictitandi Membranæ dederit. Blas. Anat. Animal. p. 2. c. 4. ex Stenon.
[Musculum Trochlearem] per intermedium trochleam traductum, nunquam intueor, quin admirabundus mecum, Ὁ Θεὸς, exclamem ὀυ μόνον ἀεὶ γεωμετρεῖ, ἀλλὰ καὶ ἀεὶ μηχανᾶται. I. C. Sturmii Exercit. Acad. 9. de Vis. Org. & Rat. c. 3. §. 4. p. 446.
[] Observare est quod Quadrupedes, qui oculos in terram pronos, ac pendulos gerunt, Musculum peculiarem habent, quo Oculi globus suspenditur——Hoc Musculo Bos, Equus, Ovis, Lepus, Porcus, &c. præditi sunt: hoc etiam Canis instruitur, sed alio modo conformatum habet. Willis de An. Brut. p. 1. c. 15.
Of this Opinion also was Bartholine Anat. l. 3. c. 8. and divers other eminent Anatomists.
But Dr. Briggs is of Opinion that the Adnata, and the other Muscles sufficiently answer all those Ends ascribed to that Muscle by former Anatomists, and thinks Probabiliùs itaque esse hunc Musculum nervi Optici actionem (per vices) confirmare, nè à prono Brutorum incessu & copioso affluxu humorum debilitetur, Ophthal. c. 2. §. 2.
The Musculus Suspensorius being in the Porpess, as well as Brutes, Dr. Tyson thinks the Use of it is not to suspend the Bulk of the Eye; but rather by its equal Contraction of the Sclerotis, to render the Ball of the Eye more or less Spherical, and so fitter for Vision. Tyson’s Anat. of the Porpess, p. 39.
[t] Musculus obliquus inferior oritur à peculiari quodam foramine in latere Orbitæ ocularis facto, (contra quam in cæteris, &c.) quo fit ut ex unâ parte à Musculo trochleari, ex alterâ verò ab hujus Musculi commodissimâ positione, Oculus in æquilibrio quodam constitutus, irretorto obtutu versus objecta feratur, nec plus justo accedat versus internum externumve canthum; quæ quidem Libratio omnino nulla fuisset, absque hujus Musculi peculiari originatione (cujus ratio omnes hucusque Anatomicos latuit). And so this curious Anatomist goes on to shew farther the stupendous Artifice of the great Creator in this Position of the Oblique Muscles. Brigg’s Nova Vis. Theor. p. 11. meo libro.
[] Besides those particular Motions which the Eye receives from the Oblique Muscles, and I may add its Libration also in some Measure, some Anatomists ascribe another no less considerable Use to them; namely, to lengthen and shorten the Eye (by squeezing and compressing it) to make it correspond to the Distances of all Objects, according as they are nigh or far off. Thus the ingenious Dr. Keil; The Aqueous Humour being the thinnest and most liquid, easily changeth its Figure, when either the Ligamentum Ciliate contracts, or both the Oblique Muscles squeeze the middle of the Ball of the Eye, to render it Oblong when Objects are too near us. Keil’s Anat. Chap. 4. Sect. 4. See [Note (y).]
[w] Quis verò opifex præter Naturam, quâ nihil potest esse callidiùs, tantam solertiam persequi potuisset in Sensibus? quæ primùm Oculos membranis tenuissimis vestivit, & sepiit; quas primum perlucidas fecit, ut per eas cerni posset: firmas aurem, ut continerentur. Cic. de Nat. Deor. l. 2. c. 57.
[x] Boyl of Final Causes.
[y] It is easy to be observed, that the Pupil openeth in dark Places; as also when we look at far distant Objects, but contracts by an Increase of Light, and when the Objects are nigh. This Motion of the Pupil some say, is effected by the circular and strait Fibres of the Uvea, and some attribute it to the Ligamentum Ciliare. Yet I have no great doubt but that they both concur in that Action, and that the Ligamentum Ciliare doth, at the same time the Pupil opens or shuts, dilate or compress the Crystalline, and bring it nigher unto, or carry it farther off the Retina. For the Structure of the Ligamentum Ciliare, and its two Sorts of Fibres, drawn with the Help of a Microscope, I shall refer to Mr. Cowper’s Anat. T. 11.
[z] In Bove, Caprâ, Equo, Ove, & quibusdam aliis elliptica est (Pupilla) ut eo magis in hisce forsan animalibus, quæ prono incessu victum in agris quæritant, radios laterales ad mala & incommoda utrinque devitanda admittat. Briggs’s Ophthal. c. 7. §. 6.
Homini erecto, aliisque, &c. caput erigere, & quaquaversus circumspicere solitis, plurima simul objecta, tum suprà, tum infrà, tum è latere utroque——visu excipiuntur; quapropter Oculi Pupilla rotunda esse debet.——Attamen bovi, &c. caput ferè semper pronum——gerentibus, tantùm quæ coràm, & paulo à latere obversantur, intuitu opus est: quapropter Pupilla——oblonga est, &c. Willis de Anim. Brut. p. 1. c. 15.
[aa] Thus Cats (their Pupils being erect, and the shutting of their Eye-lids transverse thereunto) can so close their Pupil, as to admit of, as it were, one only single Ray of Light; and by throwing all open, they can take in all the faintest Rays. Which is an incomparable Provision for these Animals, that have occasion to watch and way-lay their Prey both by Day and Night.
[bb] There is besides this large opening of the Pupil, in some nocturnal Animals, another admirable Provision, enabling them to catch their Prey in the Dark; and that is a Radiation of the Eyes: Of which Dr. Willis thus; Hujus usus est Oculi Pupillam, quasi jubare insito, illuminare, ut res noctu, & in tenebris positas conspicere valeat: quare in Fele plurimùm illustris est: at Homini, Avibus, & Piscibus deest. This Illumination he speaks of, is from the Tapetum, in the Bottom of the Eye, or the shining of the Retina, round the optick Nerve.
Besides which, he saith, the Iris hath a Faculty also, in some, of darting out Rays of Light, so as to enable them to see in the Dark: Of which he tells this Story; Novi quendam cerebro calidiori præditum, qui post uberiorem vini generosi potum in nocte atratâ, sive tenebris profundis, literas distincte legere potuit. Cujus ratio videtur esse, quòd spiritus animales velut accensi, adeòque ab hâc Iride irradiantes, jubare infito Medium illuminabant. Willis Ibid.
Such another Thing, Pliny tells us, was reported of Tiberius Cæsar: Ferunt Tib. Cæs. nec alii genitorum mortalium, fuisse naturam, ut expergefactus noctu paulisper, haud alio modo quam luce clarâ, contueretur omnia. Nat. Hist. l. 11. c. 37.
So Dr. Briggs: Virum sanè calidæ indolis novi in Comitatu Bedfordiensi degentem, qui oculis felineis——donatus est: adeò ut epistolam——mirè admodùm in loco obscuro (ubi eadem mihi vix apparuit) perlegit. Hujus verò Oculi (nisi quod Pupillas insigniores obsinuere) ab aliorum formatione neutiquam discrepabant. Ophthal. c. 5. §. 12.
[cc] The Tunica Aranea is taken notice of by Frier Bacon, who calls it, Tela Aranea, and saith, in hâc continetur——glaciale vel Crystallinum. Rog. Bacon’s Perspect. Distinct. 2. c. 3. The wrinkling of this, and the Cornea (as the Skin is of old Persons) he thinks is the Cause of the Obscurity of the Sight in such Persons. Bacon Ib. par. 2. cap. 2. But this Tunick some deny, and others allow of: Dr. A. M. of Trinity-College, Dublin, (in his Relat. of Anat. Obs. in the Eyes of Animals, in a Letter to Mr. Boyl, Ann. 1682. annexed to his Anat. Account of the Elephant burnt in Dublin, p. 57.) affirms the Tunica Aranea, and saith, I have often seen it before ’twas exposed to the Air one Minute, notwithstanding what Dr. Briggs saith to the contrary, &c. But Dr. Briggs his Opinion is, Humor Crystallinus, nisi aeri diutiùs expositus, vel lenitèr coctus (instar lactis) cuticulam non acquirit: quæ verò impropriè, Tunica Aranea dicitur, cùm si tantùm adventitia, ut in Oculo Bovis recens execto appareat. Briggs’s Ophthalm. c. 3.
The Crystalline Humour being of a double Substance, outwardly like a Gelly, towards the Center as consistent as hard Suet, upon occasion whereof its Figure may be varied; which Variation may be made by the Ligamentum Ciliare; Dr. Grew doth, upon these Accounts, not doubt to ascribe to the Ligamentum Ciliare, a Power of making the Crystalline more Convex, as well as of moving it to, or from the Retina. See Grew’s Cosmolog. Sacr. l. 1. c. 4. Now it is certain by the Laws of Opticks, that somewhat of this is absolutely necessary to distinct Vision, inasmuch as the Rays proceeding from nigh Objects do more diverge, and those from distant Objects less: Which requires either that the Crystalline Humour should be made more Convex, or more flat; or else an Elongation, or shortning of the Eye, or of the Distance between the Crystalline Humour and the Retina.
But although Dr. Briggs (so good a Judge) denies the Tunica Crystallina, contrary to the Opinion of most former Anatomists; yet there is great Reason to conclude he was in a Mistake, in my Opinion, from the Observations of the French Anatomists, of the Crystalline of the Eye, of the Gemp or Chamois, who say, The Membrana Arachnoïdes was very thick, and hard, so that it was easily separated from the Crystallinus, p. 145.
The same Anatomists also favour the Surmise of Dr. Grew, This [Contraction of the Fibres of the Ligamentum Ciliare on one side, and Dilatation on the other] would make us think that these Fibres of the Ligamentum Ciliare, are capable of Contraction, and voluntary Dilatation, like that of the Fibres of the Muscles; and that this Action may augment, or diminish the Convexity of the Crystallinus, according as the Need which the Distance of the Objects may make it to have on the Eye, to see more clearly and distinctly. Anat. Descrip. of a Bear, p. 49.
Since my penning the foregoing Notes, having as critically as I could, dissected many Eyes of Birds, Beasts and Fishes, I manifestly found the Membrana Arachnoïdes, and will undertake to shew it any one, with great Ease and Certainty. It is indeed so transparent, as not to be seen distinct from the Crystalline. But if the Cornea and Uvea be taken off before, or the vitreous Humour behind it, and the out-side of the Crystalline be gently cut, the Arachnoïdes may be seen to open, and the Crystalline will easily leap out, and part from the Ligamentum Ciliare; which otherwise it would not do: For it is by the Arachnoïdes braced to the Ligamentum Ciliare. This Membrane or Tunick, in the Ox, is so substantial and strong, though thin, that it yields to, or sinks under the sharpest Lancet, and requires (for so thin and weak a Membrane in appearance) a strong Pressure to pierce it.
[dd] As Birds and Fishes are in divers Things conformable, so in some sort they are in their Eye; to enable it to correspond to all the Convergences, and Divergences of the Rays, which the Variations of each of the Mediums may produce. For this Service the Tunica Choroeides, (in Fishes) hath a musculous Substance at the Bottom of it, lying round the optick Nerve, at a small Distance from it; by which Means I imagine they are able to contract, and dilate the Choroeides, and thereby to lengthen and shorten the Eye: For the helping in which Service, I imagine it is that the Choroeides, and Sclerotica, are in a great Measure parted, that the Choroeides may have the greater Liberty of acting upon the Humours within.
But in Birds, I have my self found, that although the Choroeides be parted from the Sclerotica; yet the Choroeides hath no Muscle, but instead thereof, a curious pectinated Work, seated on the optick Nerve, represented in [Fig. 2.] In which c.a.e.b.d. represents the Choroeides and Sclerotica: a.b. the Part of the optick Nerve, that is within the Eye: v.v.v. the vitreous Humour: a.f.g.b. the Pecten: h.i. the Crystalline. For the Reception of this Pecten, the optick Nerve comes farther within the Eye, than in other Creatures. The Structure of this Pecten, is very like that of the Ligamentum Ciliare; and in the Eye of a Magpy, and some others, I could perceive it to be musculous towards the Bottom. This Pecten is so firmly fixed unto, or embodied in the vitreous Humour, that the vitreous Humour hangs firmly to it, and is not so easily parted from it. By which Means all the Motions of the Pecten are easily communicated to the vitreous Humour, and indeed to all contained in the Choroeides. And forasmuch as the Crystalline is connected to the vitreous Humour, therefore also the Alterations in the vitreous Humour affect also the Crystalline; and the Crystalline is hereby brought nearer unto, or farther from the Retina, as occasion is. Besides all which Observables in the Choroeides, and inner Eye, I have also found this farther remarkable in the Sclerotica, and outer-part of the Eye of Birds, viz. That the fore-part of the Sclerotica is horny and hard, the middle-part thin and flexible, and Braces intervene between the fore and hind-part, running between the Choroeides and Sclerotica; by which Means the Cornea, and back-part of the Eye, are brought to the same Conformity, that the rest of the Eye hath.
The great End and Design of this singular and curious Apparatus in the Eyes, both of Birds and Fishes, I take to be, 1. To enable those Creatures to see at all Distances, far off, or nigh; which (especially in the Waters) requireth a different Conformation of the Eye. In Birds also, this is of great Use, to enable them to see their Food at their Bill’s End, or to reach the utmost Distances their high Flights enable them to view; as to see over great Tracts of Sea or Land, whither they have occasion to fly; or to see their Food or Prey, even small Fishes in the Waters, and Birds, Worms, &c. on the Earth, when they sit upon Trees, high Rocks, or are hovering high in the Air. 2. To enable those Animals to adapt their Eye to all the various Refractions of their Medium. Even the Air it self varies the Refractions, according as it is rarer or denser, more or less compressed; as is manifest from the learned and ingenious Mr. Lowthorp’s Experiment in Phil. Trans. Nᵒ. 257. and some other Experiments since of the before-commended Mr. Hawksbee, both in natural, rarify’d and compressed Air; in each of which, the Refractions constantly varied in exact Proportion to the Rarity or Density of the Air. Vid. Hawksbee’s Exp. pag. 175, &c.
Besides this Conformity in general, between the Eyes of Birds and Fishes, Du Hamel tells us of a singular Conformity in the Cormorant’s Eye, and that is, that the Crystalline is globous, as in Fishes, to enable it to see and pursue its Prey under Water: Which J. Faber, in Mr. Willoughby saith, they do with wonderful Swiftness, and for a long Time. Will. Ornithol. p. 329.
[ee] The Crystalline Humour, when dry’d, doth manifestly enough appear to be made up of many very thin spherical Laminæ, or Scales lying one upon another. Mr. Lewenhock reckons there may be 2000 of them in one Crystalline, from the outermost to the Center. Every one of these Scales, he saith, he hath discovered to be made up of one single Fibre, or finest Thread wound, in a most stupendous Manner, this way, and that way, so as to run several Courses, and meet in as many Centers, and yet not to interfere, or cross one another, in any one Place. In Oxen, Sheep, Hogs, Dogs and Cats, the Thread spreads into three several Courses, and makes as many Centers: In Whales five; but in Hares and Rabbets only two. In the whole Surface of an Ox’s Crystalline, he reckons there are more than 12000 Fibres juxtaposited. For the right and clear Understanding of the Manner of which admirable Piece of Mechanism, I shall refer to his Cuts and Descriptions in Philos. Trans. Nᵒ. 165. and 293. The Truth hereof I have heard some ingenious Men question; but it is what I my self have seen, and can shew to any Body, with the Help of a good Microscope.
[ff] S. Malpighi observed the Middle of the optick Nerve of the Sword-Fish, to be nothing else but a large Membrane, folded according to its Length in many Doubles, almost like a Fan, and invested by the Dura mater; whereas in Land-Animals it is a Bundle of Fibres. V. Phil. Trans. Nᵒ. 27.
[gg] Certissimum est, quòd in omnibus Oculis humanis (quos saltem mihi dissecare contigit) Nervus opticus Pupillæ è diametro apponitur, &c. Briggs’s Ophthal. c. 3. §. 15. Ita Willis de Anim. Brut. p. 1. c. 15.
Nervi Optici in nobis, item in Cane, Fele (& in cateris forsan animalibus calidis) ad fundum Oculi delati Pupilla regioni prospiciunt, dum interim in aliis Quadrupedibus, uti etiam in Piscibus & Volueribus, obliquè semper Tunica Sclerotidi inseruntur. Unde, &c. Willis Ib. c. 7. §. 11.
[hh] This Pair is united at its Rise; whence is commonly drawn a Reason why one Eye being mov’d towards an Object, the other is directed also to the same. Gibson’s Anat. Book III. Chap. 11. So Bartholine Anat. Libellus 3. c. 2.
[ii] Among all the other Security the Eye hath, we may reckon the Reparation of the aqueous Humour; by which Means the Eye when wounded, and that in all Appearance very dangerously too, doth often recover its Sight: Of which Bern. Verzascha gives divers Examples ancient and modern. One is from Galen, of a Boy so wounded, that the Cornea fell, and became flaccid, but yet recovered his Sight. Other such like Instances also he gives from Realdus Columbus, Rhodius, and Tulpius; and one that he cured himself in these Words, Ego in Nobilissimi viri filiolâ similem casum observavi: hæc dum levibus de causis cum fratre altercaret, iste iracundiâ percitus cultellum Scriptorium apprehendit, & sororis oculo vulnus infligit, inde humor aqueus effluxit. Vocatus præsentem Chirurgum jussi sequens collyrium anodynum & exsiccans tepidè sæpiùs admovere. ℞ aq. Plantag. ℥iv. Rosar. Sanicul. Euphras. ana Trochisc. alb. Rhaf. cum Opio ℈ii. Tutiæ pp. ℈i. Croci orient. ℈ss. M. Hoc Collyrium inflammationem compescuit, vulnus siccavit & sanavit. Hinc post aliquot menses Humor aqueus succrevit. Nam visus, sed dibilior, cum summo parentum gaudio redivit. B. Verzaschæ Observ. Medicæ. Obs. 14.
Another Cure of this kind, was experimented by Dr. Daniel Major, upon a Goose, Ann. 1670, the aqueous Humour of both whose Eyes they let out, so that the Eyes fell, and the Goose became quite blind: But without the Use of any Medicine, in about two Days Time, Nature repaired the watery Humour again, the Eyes returned to their Former Turgency, and the Goose was in a Week after produced seeing before twenty eight or thirty Spectators. Ephem. Germ. T. 1. Add. ad. Obs. 117.
From the same Cause, I doubt not, it was that the Eye of a Gentleman’s Daughter, and those of a Cock, when wounded, so that the Cornea sunk, were restored by a Lithuanian Chymist, that passed for a Conjurer, by the Use of a Liquor found in May, in the Vesiculæ of Elm. Of which see Mr. Ray’s Catal. Cantab. in Ulmus from Henr. ab Heers.
[kk] Palpebræ, quæ sunt tegumenta Oculorum, mollissimæ tactu, nè lederent aciem, aptissimæ factæ, & ad claudendas Pupillas, nè quid incideret, & ad aperiendas; idque providit, ut identidem fieri posset cum maximâ celeritate. Munitæque sunt Palpebræ tanquàm vallo pilorum: quibus & apertis Oculis, si quid incideret, repelleretur, & somno conniventibus, cùm Oculis ad cernendum non egerimus, ut qui, tanquàm involuti, quièscerent. Latent prætereà utiliter, & excelsis undique partibus sepiuntur. Primùm enim superiora Superciliis obducta sudorem à capitæ, & fronte destuentem repellunt. Genæ deinde ab inferiore parte tutantur subjectæ, leviterque eminentes. Cicer. de Nat. Deor. L. 2. c. 57.
Tully, in the Person of a Stoick, having so well accounted for the Use of the Eye-Lids, I shall for a further Manifestation of the Creator’s Contrivance and Structure of them, take notice of two or three Things: 1. They consist of a thin and flexible, but strong Skin, by which means they the better wipe, clean, and guard the Cornea. 2. Their Edges are fortified with a soft Cartilage, by which means they are not only enabled the better to do their Office, but also to close and shut the better. 3. Out of these Cartilages grow a Pallisade of stiff Hairs, of great Use to warn the Eye of the Invasion of Dangers, to keep off Motes, and to shut out too excessive Light, &c. and at the same time to admit of (through their Intervals) a sufficient Passage for Objects to approach the Eye. And it is remarkable, that these Hairs grow but to a certain, commodious Length, and need no cutting, as many other Hairs of the Body do: Also, that their Points stand out of the way, and in the upper-lid bend upwards, as they do downwards in the lower lid, whereby they are well adapted to their Use. From which last Observables, we may learn how critical and nice the great Author of Nature hath been, in even the least and most trivial Conveniencies belonging to Animal Bodies; for which Reason I have added it to Tully’s Remarks. And more might have been added too, as particularly concerning the curious Structure and Lodgment of the Right Muscle, which opens the Eye-Lids; and the Orbicularis, or Circular one, that shuts them; the nice Apparatus of Glands that keep the Eye moist, and serve for Tears; together with the Reason why Man alone, who is a social Animal, doth exhibit his social Affections by such outward Tokens as Tears; the Nerves also, and other Organs acting in this Ministry. I might also speak of the Passages for discharging the superfluous Moisture of the Eyes through the Nostrils, and much more of the like kind. But it would take up too much Room in these Notes; and therefore it shall suffice to give only such Hints as may create a Suspicion of a noble Œconomy and Contrivance in this (I had almost said) least considerable part of the Eye. But for Particulars I shall refer to the Anatomists; and for some of these Things, particularly to Dr. Willis’s Cereb. Anat. and de Anim. Brut. and Mr. Cowper’s Elegant Cuts in the 11ᵗʰ Tab. of his Anatomy.
To the Eye-Lids we may add another Guard afforded the Eyes of most Quadrupeds, Birds, and Fishes, by the nictitating Membrane, which Dr. Willis gives this Account of, Plurimis [Animalibus] quibus Musculus suspensorius adest (which Limitation he needed not to have added) etiam alter Membranosus conceditur, qui juxta interiorem oculi canthum situs, quando elevatur, Oculi globum ferè totum obtegit. Hujus usus esse videtur, ut cùm Bestiæ inter gramina, &c. capita sua propter victum capessendum demergunt, hic Musculus Oculi Pupillam, nè à stipularum incursu seriatur, oculit, munitque. De Anim. Brut. p. 1. c. 15.
This Membrane Man hath not, he having little Occasion to thrust his Head into such Places of Annoyance, as Beasts and other Animals; or if he hath, he can defend his Eyes with his Hands. But Birds (who frequent Trees and Bushes) and Quadrupeds, (Hedges and long Grass) and who have no part ready, like the Hand, to fence off Annoyances; these, I say, have this incomparable Provision made for the Safety of their Eyes. And for Fishes, as they are destitute of Eye-Lids, because in the Waters there is no occasion for a Defensative against Dust and Motes, offensive to the Eyes of Land Animals, nor to moisten and wipe the Eyes, as the Eye-Lids do, so the Nictitating-Membrane is an abundant Provision for all their Occasions, without the Addition of the Eye-Lids.
And now, if we reflect, are these the Works of any Thing but a wise and indulgent Agent?
[ll] Although the Hardness and Firmness of the Adnata, or Sclerotica in Birds, is a good Guard to their Eyes, yet I do not think it is made thus, so much for a Defence, as to minister to the lengthning and shortning the Eye, mentioned before in [Note (cc).]
[mm] Cochleis oculorum vicem Cornicula bina pratentu implent. Plin. Nat. Hist. l. 11. c. 37. See more of the Eyes of Snails before in [Note (k)]; and in [Note (l)], I said that I suspected Moles also might thrust out, or withdraw their Eyes more or less within the Hair or Skin.
[nn] The diligent Sturmius was fully persuaded there could not be any speculative Atheism in any one that should well survey the Eye. Nobis, saith he, fuit persuasissimum. Atheismum, quem vocant speculativum, h. e. obsirmatam de Deitate in Universo nullâ persuasionem, habere locum aut inveniri non posse in eo homine, qui vel unius corporis organici, & speciatim Oculi fabricam attento animo aspexerit. Sturm. Exerc. Acad. 9. De Vis. Organ. & Rat. in Epilogo.
[oo] The glorious Landskips, and other Objects that present themselves to the Eye, are manifestly painted on the Retina, and that not erect, but inverted as the Laws of Opticks require; and is manifest to the Eye from Monsieur Cartes’s Experiment, of laying bare the vitreous Humour on the back part of the Eye, and clapping over it a Bit of white Paper, or the Skin of an Egg; and then placing the fore-part of the Eye to the Hole of the Window of a darkned Room. By which means we have a pretty Landskip of the Objects abroad invertedly painted on the Paper, on the back of the Eye. But now the Question is, How in this Case the Eye comes to see the Objects erect? Monsieur Cartes’s Answer is, Notitia illius ex nullâ imagine pendet, nec ex ullâ actione ab objectis veniente, sed ex solo situ exiguarum partium cerebri, è quibus Nervi expullulant.——E.g. cogitandum in Oculo——situm capillamenti nervi optici——respondere ad alium quendam partis cerebri——qui facit ut Anima singula loca cognoscat, quæ jacent in rectâ, aut quasi rectâ lineæ; ut ita mirari non debeamus corpora in naturali situ videri, quamvis imago in oculo delineata contrarium habeat. Dioptr. c. 6. But our most ingenious Mr. Molyneux answereth thus, The Eye is only the Organ or Instrument, ’tis the Soul that sees by means of the Eye. To enquire then how the Soul perceives the Object erect, by an inverted Image, is to enquire into the Soul’s Faculties——But erect and inverted are only Terms of Relation to up and down; or farther from, or nigher to the Center of the Earth, in Parts of the same Thing.——But the Eye, or visive Faculty takes no notice of the internal Posture of its own Parts, but useth them as an Instrument only, contrived by Nature for the Exercise of such a Faculty.——Let us imagine, that the Eye (on its lower Part) receives an Impulse [by a Ray from the upper part of the Object] must not the visive Faculty be necessarily directed hereby to consider this Stroke, as coming from the top rather than the bottom [of the Object] and consequently be directed to conclude it the Representation of the top? Hereof we may be satisfied, by supposing a Man standing on his Head. For here, though the upper Parts of Objects are painted on the upper Parts of the Eye, yet the Objects are judged to be erect. What is said of Erect and Reverse, may be understood of Sinister and Dexter. Molyneux’s Dioptr. Nov. Part I. Prop. 28.
CHAP. III.
Of the Sense of Hearing.
Concerning the Sense of Hearing, I shall take notice of two Things, the Organ, the Ear; and its Object, Sound.
I. For the Organ, the Ear; I shall pass by its convenient Number of being double, which (as in the last Sense) serves for the commodious Hearing every way round us; as also a wise Provision for the utter Loss or Injury[a] of one of the Ears. But I shall a little insist upon its Situation, and its admirable Fabrick and Parts.
1. It is situated in the most convenient Part of the Body, (like as I said the Eye is) in a Part near the common Sensory in the Brain, to give the more speedy Information; in a Part where it can be best guarded, and where it is most free from Annoyances and Harms it self, and where it gives the least Annoyance and Hindrance to the Exercises of any other Part; in a Part appropriated to the peculiar Use of the principal Senses, in the most lofty, eminent Part of the Body, where it can perceive the most Objects, and receive the greatest Information: And lastly, in a Part in the Neighbourhood of its Sister Sense the Eye, with whom it hath peculiar and admirable Communication by its Nerves, as I intend to shew in its proper Place. In respect then of its Situation and Place in the Body, this Sense is well designed and contrived, and may so far be accounted the Work of some admirable Artist. But,
2. If we survey its Fabrick and Parts, it will appear to be an admirable Piece of the Divine Wisdom, Art, and Power. For the Manifestation of which, let us distinctly survey the outward and the inward Part of its curious Organ.
1. For the outward Ear: If we observe its Structure in all Kinds of Animals, it must needs be acknowledged to be admirably Artificial, it being so nicely prepared, and adjusted to the peculiar Occasions of each respective Animal. In Man[], it is of a Form proper for the erect Posture of his Body. In Birds, of a Form proper for Flight; not protuberant, because that would obstruct their Progress, but close and covered, to afford the easier Passage through the Air. In Quadrupeds, its Form is agreeable to the Posture, and slower Motion of their Bodies; and in these too, various, according to their various Occasions. In some large, erect, and open, to hear the least Approaches of Dangers[c], in others covered, to keep out noxious Bodies. In the Subterraneous Quadrupeds, who are forced to mine, and dig for their Food and Habitation, as a protuberant Ear, like that of other Quadrupeds, would obstruct their Labours, and be apt to be torn and injured; so they have the contrary[d], their Ears short, lodged deep and backward in their Head, and passing to the under Part thereof, and all sufficiently fenced and guarded. And as for Insects, Reptiles, and the Inhabitants of the Waters, if they enjoy this Sense, (as there is great Reason to think they do,) it may probably be lodged commodiously under the same Security and Guard, as the Smelling, or some other Sense is.
And moreover, as the Form of this Organ is various in various Animals, so in each of them its Structure is very curious and observable, being in all admirably contrived to collect the wandering, circumambient Impressions, and Undulations of Sound, and to convey them to the Sensory within. If I should run over the several Genera of Animals, we might find a notable Prospect of the handy-work of God[e], even in this so inconsiderable Part of Animals. But I shall only carry my Survey to that of Man. And here the first Thing that offereth it self to our View, is the Helix, with its tortuous Cavities, made to stop, and collect the sonorous Undulations, to give them a gentle Circulation and Refraction, and so convey them to the Concha, or larger and more capacious round Cell at the Entrance of the Ear. And to bridle the Evagation of the Sound, when arrived so far, but withal not to make a Confusion thereof, by any disagreeable Repercussions, we may take notice of a very curious Provision in those little Protuberances, called the Tragus, and Antitragus of the outward Ear, of a commodious Form and Texture[f], and conveniently lodged for this Use. The great Convenience and Benefit of this Form and Contrivance of the outward Ear, is sufficiently manifest by the want thereof, which causeth a Confusion in the Hearing, with a certain Murmur, or Swooing like the Fall of Waters[g].
Another wise Provision of the Creator, is in the Substance of the outward Ear, which is cartilaginous, the fittest for this Place. For (as an ingenious Anatomist[h] observes) “If it had been Bone, it would have been troublesome, and might by many Accidents have been broken off: If Flesh, it would have been subject to Contusion”. But indeed a worse Consequence than this would have ensu’d such a Softness as that of Flesh, and that is, it would neither have remain’d expanded, neither would it so kindly receive and circulate the Sounds, but absorb, retard, or blunt their Progress into the inward Organ. But being hard, and curiously smooth and tortuous, Sounds find an easie Passage, with a regular Volutation and Refraction: As in a well-built Arch, Grotto, or musical Instrument, which magnify and meliorate Sounds; and some of which convey even a Whisper to a large Distance[]: But from the outward, let us carry our Survey,
2. To the inward Part of this admirable Organ. And here we find the most curious and artful Provision for every Emergency and Occasion. The auditory Passage, in the first Place, curiously tunnelled, and artfully turned, to give Sounds an easie Passage, as well as a gentle Circulation and Refraction; but withal, so as to prevent their too furious rushing in, and assaulting the more tender Parts within.
And forasmuch as it is necessary that this Passage should be always open, to be upon the Watch[k]; therefore to prevent the Invasion of noxious Insects, or other Animals, (who are apt to make their retreat in every little Hole), Nature hath secured this Passage[l], with a bitter nauseous Excrement[m], afforded from the Glands[n] appointed for that Purpose.
From hence let us approach the most inward Parts, in which we shall see Strokes of the most exquisite Art. To pass over the innate Air, that most Authors talk of[o], (because there is no such) the passage to the Palate[p], and their Uses, with divers other curious Things that might be named; let us stop a little at the Part containing the rest, namely, the Bone[q]. The particular Texture and Hardness of which, above other Bones of the Body, is very remarkable; whereby it serves not only as a substantial Guard to the Sensory, but also to oppose the Impulses of the ætherial Matter, that there may be no loss, nor Confusion in the Sound; but that it may be conveyed regularly, and intirely to the auditory Nerves.
The next Part I shall take Notice of, may be that fine Membrane, called the Tympanum, or Membrana Tympani[r], with its inner Membrane[]; together with the four little appendent Bones[t], and the three inner Muscles to move them, and adjust the whole Compages to the several Purposes of Hearing, to hear all Manner of Sounds, loud or languid, harsh or grateful[].
From this Region of the Tympanum, I might pass to that of the Labyrinth[w], and therein survey the curious and admirable Structure of the Vestibulum, the Semicircular Canals[x], and Cochlea; particularly the artificial Gyrations, and other singular Curiosities observable in the two latter.
But I shall not expatiate on these recluse Parts; only there is one special Contrivance of the Nerves, ministring to this Sense of Hearing, which must not be passed by; and that is, the Branches of one of the auditory Nerves[y], spread partly to the Muscles of the Ear, partly to the Eye, partly to the Tongue and Instruments of Speech, and inosculated with the Nerves to go to the Heart and Breast. By which Means there is an admirable, and useful Content between these Parts of the Body; it being natural for most Animals, upon the Hearing any uncouth Sound, to erect their Ears, and prepare them to catch every Sound; to open their Eyes (those constant faithful Sentinels) to stand upon their Watch; and to be ready with the Mouth to call out, or utter what the present Occasion shall dictate. And accordingly it is very usual for most Animals, when surpriz’d, and terrify’d with any Noise, presently to shriek and cry out.
But there is besides this, in Man, another great Use of this nervous Commerce between the Ear and Mouth: And that is, (as one of the best Authors on this Subject expresseth it)[z], “That the Voice may correspond with the Hearing, and be a kind of Echo thereof, that what is heard with one of the two Nerves, may be readily expressed with the Voice, by the help of the other.”
Thus much shall suffice to have spoken concerning the Organ. Let us,
II. Take Notice of the Object of this admirable Sense, namely, Sound; and so conclude this Chapter. I shall not here enquire into the Nature and Properties of Sound, which is in a great Measure intricate, and hath puzzelled the best Naturalists: Neither shall I shew how this admirable Effect of the divine Contrivance, may be improv’d to divers Uses[aa] and Purposes in humane Life; but my Business will be to shew that this Thing, of so admirable Use in the animal World, is the Work of God. And this will appear, let the subject Matter of Sounds be what it will; either the Atmosphere[bb] in Gross, or the ætherial Part thereof, or soniferous Particles of Bodies, as some fancy, or whatever else the Philosopher may think it. For who but an intelligent Being, what less than an omnipotent and infinitely wise God could contrive, and make such a fine Body, such a Medium, so susceptible of every Impression, that the Sense of Hearing hath occasion for, to empower all Animals to express their Sense and Meaning to others; to make known their Fears, their Wants, their Pains and Sorrows in melancholick Tones; their Joys and Pleasures in more harmonious Notes; to send their Minds at great Distances[cc], in a short Time[dd], in loud Boations; or to express their Thoughts near at hand with a gentle Voice, or in secret Whispers! And to say no more, who less than the same most wise and indulgent Creator, could form such an Oeconomy, as that of Melody and Musick is! That the Medium should (as I said) so readily receive every Impression of Sound, and convey the melodious Vibration of every musical String, the harmonious Pulses of every animal Voice, and of every musical Pipe; and the Ear be as well adapted, and ready to receive all these Impressions, as the Medium to convey them: And lastly, that by Means of the curious Lodgment, and Inosculations of the auditory Nerves before-mentioned, the Orgasms of the Spirits should be allay’d, and Perturbations of the Mind, in a great Measure quieted and stilled[ee]: Or to express it in the Words of the last-cited famous Author[ff], “That Musick should not only affect the Fancy with Delight; but also give Relief to the Grief and Sadness of the Heart; yea, appease all those turbulent Passions, which are excited in the Breast by an immoderate Ferment, and Fluctuation of the Blood”.
And now, who can reflect upon all this curious Apparatus of the Sense of Hearing, and not give the great Creator his due Praise! Who can survey all this admirable Work, and not as readily own it to be the Work of an omnipotent, and infinitely wise and good GOD[gg], as the most artful Melodies we hear, are the Voice or Performances of a living Creature!
