Of the Heart of Quadrupeds.
In this Part there is a notable Difference found between the Heart of Man and that of Beasts, concerning the latter, of which I might take notice of the remarkable Confirmation of the Hearts of Amphibious Quadrupeds, and their Difference from those of Land-Animals, some having but one Ventricle[a], some three[], and some but two (like Land-Animals) but then the Foramen Ovale therewith[c]. All which may be justly esteemed as wonderful, as they are excellent Provisions for the Manner of those Animals living. But I shall content my self with bare Hints of these Things, and speak only of two Peculiars more, and that but briefly.
One is the Situation of the Heart, which in Beasts is near the middle of the whole Body; in Man, nearer the Head[d]. The Reasons of which I shall give from one of the most curious Anatomists of that Part[e]. “Seeing, saith he, the Trajection and Distribution of the Blood depends wholly on the Systole of the Heart, and that its Liquor is not driven of its own Nature so readily into the upper Parts as into Vessels even with it, or downwards into those under it: If the Situation of the Heart had been further from the Head, it must needs either have been made stronger to cast out its Liquor with greater Force; or else the Head would want its due Proportion of Blood. But in Animals that have a longer Neck, and which is extended towards their Food as it were, the Heart is seated as far from the other Parts; and they find no Inconvenience from it, because they feed with their Head for the most part hanging down; and so the Blood, as it hath farther to go to their Head than in others, so it goes a plainer and often a steep Way[f].”
The other peculiar Matter is, the fastning (I formerly mentioned) which the Cone of the Pericardium hath in Man to the Diaphragm[g], whereas in all Quadrupeds it is loose. By which Means the Motion of the Midriff, in that necessary Act of Respiration, is assisted both in the upright Posture of Man, as also in the prone Posture of Quadrupeds[h]; which would be hindred, or rendred more difficult, if the Case was otherwise: “Which must needs be the Effect of Wisdom and Design, and that Man was intended by Nature to walk erect, and not upon all-four, as Quadrupeds do:” To express it in the Words of a great Judge in such Matters [].
FOOTNOTES:
[a] Frogs are generally thought to have but one Ventricle in their Hearts.
[] The Tortoise hath three Ventricles, as the Parisian Academists in their Memoirs affirm. Besides these two Ventricles [before spoken of] which were in the hinder Part of the Heart, which faceth the Spine; there was, say they, a third in the Fore-part, inclining a little towards the Right-side, &c. Memoirs, &c. p. 259. But Mr. Bussiere charges this as a Mistake in those ingenious Gentlemen, and asserts there is but one Ventricle in the Tortoise’s Heart. See his Description of the Heart of the Land Tortoise, in Philos. Transact. Nᵒ. 328.
[c] The Sea-Calf is said by the French Academists, to have this Provision, and their Account of it is this: Its Heart was round and flat. Its Ventricles appeared very large, and its Auricles small.——Underneath the great Aperture, through which the Trunk of the Vena Cava conveyed the Blood into the right Ventricle of the Heart, there was another, which penetrated into the Arteria Venosa, and from thence into the left Ventricle, and afterwards into the Aorta. This Hole called the Foramen Ovale in the Fœtus, make the Anastomisis, by the Means of which, the Blood goes from the Cava into the Aorta, without passing through the Lungs. French Anatomists, p. 124.
[d] Τὴν τε Καρδίαν περὶ τὸ μέσον πλὴν ἐν ἀνθρώπῳ, &c. Arist. Hist. An. L. 2. c. 17.