Note d — BOOK IV.

It is remarkable in the Joynts, and a manifest Act of Caution and Design, 1. That altho’ the Motion of the Limbs be circular, yet the Center of that Motion is not in a Point, but an ample Superficies. In a Point, the Bones would wear and penetrate one another; the Joynts would be exceedingly weak, &c. but the Joynts consisting of two large Superficies, Concave and Convex, some furrowed and ridged, some like a Ball and Socket, and all lubricated with an oily Substance, they are incomparably prepared both for Motion and Strength. 2. That the Bones next the Joynt are not spungy, as their Extremities commonly are, nor hard and brittle, but capped with a strong, tough, smooth, cartilaginous Substance, serving both to Strength and Motion.

But let us here take notice of what Galen mentions on this Subject. Articulorum unusquisque Eminentiam Cavitati immissam habet: Veruntamen hoc fortasse non adeò mirabile est: Sed si, consideratâ omnium totius corporis ossium mutuâ connexione, Eminentias cavitatibus suscipientibus æquales semper inveneris; Hoc mirabile. Si enim justo amplior esset Cavitas, laxus sanè & infirmus fieret Articulus; si strictior, motus difficulter fieret, ut qui nullam versionem haberet; ac periculum esset non parvum, eminintias ossium arctatas frangi: sed horum neutrum factum est.——Sed quoniam ex tam securâ constructione periculum erat, nè motiones difficiliùs fierent, & eminentiæ ossium extererentur, duplex rursus auxilium in id Natura molita est. 1. Cartilagine os utrumque subungens, atque oblinens: alterum, ipsis Cartilaginibus humorem unctuosum, velut oleum, superfundens; per quem facilè mobilis, & attritu contumax omnis articulatio Ossium facta est.——Ut undique diligenter Articulus omnis custodiretur, Ligamenta quædam ex utroque osse produxit Natura. Galen de Us. Part. l. 1. c. 15.