It is remarkable, that in Man, the Head is of one singular Form; in the four-footed Race, as various as their Species. In some square and large, suitable to their slow Motion, Food, and Abode; in others less, slender, and sharp, agreeable to their swifter Motion, or to make their Way to their Food[a], or Habitation under Ground[b]. But passing by a great many Observations that might be made of this Kind, I shall stop a little at the Brain, as the most considerable Part of this part of the Body, being the great Instrument of Life and Motion in Quadrupeds, as ’tis in Man of that, as also in all Probability the chief Seat of his immortal Soul. And accordingly it is a remarkable Difference, that in Man the Brain is large, affording Substance and Room for so noble a Guest; whereas in Quadrupeds, it is but small. And another Thing no less remarkable, is the Situation of the Cerebrum and Cerebellum, or the greater or lesser Brain, which I shall give in the Words of one of the most exact Anatomists we have of that Part[c]: “Since, saith he, God hath given to Man a lofty Countenance, to behold the Heavens, and hath also seated an immortal Soul in the Brain, capable of the Contemplation of heavenly Things; therefore, as his Face is erect, so the Brain is set in an higher Place, namely, above the Cerebellum and all the Sensories. But in Brutes, whose Face is prone towards the Earth, and whose Brain is capable of Speculation, the Cerebellum, (whose Business it is to minister to the Actions and Functions of the Præcordia, the principal Office in those Creatures) in them is situated in the higher Place, and the Cerebrum lower. Also some of the Organs of Sense, as the Ears and Eyes, are placed, if not above the Cerebrum, yet at least equal thereto.”
Another Convenience in this Position of the Cerebrum and Cerebellum, the last ingenious Anatomist[d] tells us is this, “In the Head of Man, saith he, the Base of the Brain and Cerebell, yea, of the whole Skull, is set parallel to the Horizon; by which Means there is the less Danger of the two Brains joggling, or slipping out of their Place. But in Quadrupeds, whose Head hangs down, the Base of the Skull makes a right Angle with the Horizon, by which Means the Brain is undermost, and the Cerebell uppermost; so that one would be apt to imagine the Cerebell should not be steady, but joggle out of its Place. To remedy which Inconvenience he tells us, And lest the frequent Concussions of the Cerebell should cause a Fainting, or disorderly Motion of the Spirits about the Præcordia, therefore, by the Artifice of Nature, sufficient Provision is made in all, by the dura Meninx closely encompassing the Cerebellum; besides which, it is (in some) guarded with a strong bony Fence; and in others, as the Hare, the Coney, and such lesser Quadrupeds, a part of the Cerebell is on each Side fenced with the Os Petrosum: So that by this double Stay, its whole Mass is firmly contained within the Skull.”
Besides these Peculiarities, I might take notice of divers other Things no less remarkable, as the Nictitating Membrane of the Eye[e], the different Passages of the Carotid Arteries[f] through the Skull, their Branching into the Rete Mirabile[g], the different Magnitude of the Nates, and some other Parts of the Brain in Beasts, quite different from what it is in Man: But the Touches already given, may be Instances sufficient to prevent my being tedious in inlarging upon these admirable Works of God.
FOOTNOTES:
[a] Thus Swine, for Instance, who dig in the Earth for Roots and other Food, have their Neck, and all Parts of their Head very well adapted to that Service. Their Neck short, brawny, and strong; their Eyes set pretty high out of the Way; their Snout long; their Nose callous and strong; and their Sense of Smelling very accurate, to hunt out and distinguish their Food in Mud, under Ground, and other the like Places where it lies concealed.
[b] What hath been said of Swine is no less, rather more remarkable in the Mole, whose Neck, Nose, Eyes and Ears, are all fitted in the nicest Manner to its subterraneous Way of Life.
[c] Willis Cereb. Anat. cap. 6. Cumque huic Deus os sublime dederit, &c.
[d] Id. paulo post. In capite humano Cerebri & Cerebelli, &c.
[f] Arteria Carotis Aliquanto posterius in homine quàm in alio quovis animali, Calvariam ingreditur, scil. juxta illud foramen, per quod sinus lateralis in Venam jugularem desiturus cranio elabitur; nam in cæteris hæc arteria sub extremitate, seu processu acuto ossis petrosi, inter cranium emergit: verùm in capite humano, eadem, ambage longiori circumducta (ut sanguinis torrens, priusquam ad cerebri oram appellit, fracto impetu, leniùs & placidiùs fluat) prope specum ab ingressu sinûs lateralis factum, Calvariæ basin attingit;——& in majorem cautelam, tunicâ insuper ascititiâ crassiore investitur. And so he goes on to shew the Conveniency of this Guard the Artery hath, and its Passage to the Brain, and then saith, Si hujusmodi conformationis ratio inquiritur, facilè occurrit, in capite humano, ubi generosi affectus & magni animorum impetus ac ardores excitantur, sanguinis in Cerebri oras appulsum debere esse liberum & expeditum, &c. Atque hoc quidem respectu differt Homo à plerisque Brutis, quibus, Arteria in mille surculos divisa, ne sanguinem pleniore alveo, aut citatiore, quàm par est, cursu, ad cerebrum evehat, Plexus Retiformes constituit, quibus nempe efficitur, ut sanguis tardo admodum, lenique & æquabili fere stillicidio, in cerebrum illabatur. And then he goes on to give a farther Account of this Artery, and the Rete mirabile in divers Creatures. Willis, ibid. cap. 8.
[g] Galen thinks the Rete mirabile is for concocting and elaborating the Animal Spirits, as the Epididymides, [the Convolutions κιρσοειδοῦς ἕλικος] are for elaborating the Seed. De Us. Part. L. 9. c. 4. This Rete is much more conspicuous in Beasts than Man; and as Dr. Willis well judges, serves, 1. To bridle the too rapid Incursion of the Blood into the Brain of those Creatures, whose Heads hang down much. 2. To separate some of the superfluous serous Parts of the Blood, and send them to the Salival Glands, before the Blood enters the Brain of those Animals, whose Blood is naturally of a watery Constitution. 3. To obviate any Obstructions that may happen in the Arteries, by giving a free Passage through other Vessels, when some are stopped.
In Quadrupeds, as the Carotid Arteries are branched into the Rete Mirabile, for the bridling the too rapid Current of Blood into the Brain; so the Vertebral Arteries, are, near their Entrance into the Skull, bent into an acuter Angle than in Man, which is a wise Provision for the same Purpose.