Page:Cyclopaedia, Chambers - Volume 1.djvu/272

 BRA

fill : Thefe Brails belong only to the two Courfes and the Mizen-fail. The Word is, Hale up the Brails ; or, which is all one, Brail up the Sails ; for the Meaning is, that the Sail fliould be hilled up, in order to be fori d, or bound dole to the Yard.

BRAIN, in its general Senfe, that large, Toft, whitlfh Mais, inclos'd in the Cranium or Skull; wherein all the Organs of Senfe terminate, and the Soul is fuppofed principally to refidc. The Brain is encompafs'd with two Meninges, or Membranes, cali'd Dura and c J?ia Mater ; fee Meninges. Irs Figure is the fame with that of the Bones that contain it 5 viz. roundifh, oblong, and flat on the Sides : It is divided into three principal Parts, viz. the Cerebrum, or Brain (trictly fo cali'd, the Cerebellum, and the Medulla oblongata : The two latter of which fee under their proper Heads, Cerebrum and Medulla.

The Cerebrum, or Brain, properly fo cali'd, is that large globulous Part which fills the fore and upper Part of the Skull : It is divided by a Duplicature of the Dura Mater, cali'd from its Figure Falx, into two equal Parts, cali'd Right and Left Ucmifpheres : Tho the Figute of tha Brain be pretty far from a Sphere. It is alfo feparated from the Cerebellum by another Duplicature of the fame Dura Ma- ter. The Brain confitls of two Kinds of Subllance, the one Cineritious, or of an AfTi-colour, foft and moilt; which being the Exterior, is cali'd the Cortex, or Cortical Part of the Brain : the Thicknefs of this is about half an Inch, tho by reafon of the Sinus's and Sutures in the Brain it appears more. The other, or inner Subflance, is white, more folid, as well as more dry than the Cortex, and is cali'd the Marro-w or Medullary, and fometimes the Fi- brous Part, in contra-diltinflion to the other, which is cali'd the Glandulous Part.

The Cortex, according to Malpighi, is form'd from the minute Branches of the Carotid and Vertebral Arteries ; which being woven together in the (Pitt Mater, fend from each Point thereof, as from a Bafis, little Branches, which, being twilled together into the Form of a Gland, inclofe the Medulla, ordinarily to the Thicknefs of half an Inch ; but in fomc places make deeper Sinus's and Furrows within it. Thefe Branches make Circumvolutions like the Interlines ; each of which may be rcfolv'd into others, like, but lefs than the firfl • This Part, therefore, moll other Authors take to be Glandulous ; or, an Aflemblage of innumera- ble minute Glands, contiguous to each other, dellin'd for the Secretion of Animal Spirits from the Blood, brought hither by the Carotids, &c. Thefe Glandules, Malpighi obferves, are of themfelves oval, but by the mutual Com- preffure become angular ; they run waving within each other : Several of thefe conneflcd, form others fomewhat larger ; and thefe again unite into others, from the Aggre- gate whereof are form'd Tubes, of which the outer Cortex is compos'd. Thefe little Glands confift of the Branches of the Arteries which bring the Blood; of the Veins arifing at their Extremities, which carry it back again; of Secre- tory Tubes lecerning the Animal Spirits, and of Excrctoty Dufts for difcharging 'em into the Medulla : Tho thefe are roo minute to have ever been feen. See Cortex.

The Inner, or Medullary Part of the Brain, confitls of infinitely fine Fibres, arifing from the leaf! and minute!! Branches or Filaments of the Glands of the Cortex ; as is chfhr.clly lccn in the Cerebellum, tho fcarce vifible in the Cerebrum : Thefe receive the Fluid feparated and fubti- lu d, from the Glands of the Cottex ; and by means of the Nerves, which are no more than Produflions of this Part difttibute it all over the Body. Authors, here, however, arc divided ; the generality, with Malpighi, making the Subflance ot the Cortex Glandulous, as above ; others, with Ruyfcb and Lceztenhocck, denying any thing like Glands in it ; and allowing nothing but little Crypta, or Sinks, open- ing laterally to the Arteries ; and thence receiving a Juice already fecern'd from tho Blood, and tranfmirrino it to the Medulla. This Doctrine, it feems, is the Refult of Ana- tomical Injections and Microfcopical Ob'fervations ; but the other appearing tho moll confident with the Occonomy of Nature in other things, is generally adhcr'd to. '

The Cortex covers the whole Medullaty Subllance K° •, '<., n Snm and Cerebellum; fo as wherever the Cortical Subflance ends, there the Medullary commences ; and this rn the Appendices, Ventticles, Interfliccs, and Si' mis sot the Medulla, as well as in the External Surface. Something Medullary, therefore, arifing from every Point of toe Cortex; at its firfr rife, it mufl needs be exceedingly fine and (lender : But being join'd with other Parts of trie lame kind, it gradually thickens, and at length becoming lenfiole, conftmues jhe Medulla Cerebri, the Corpus Cat lojhm, the Medulla oblongata and its Legs, the Tha'l'ami of the Optic Nerves, the Medulla Cerebelii, and its Produc- tion into the Medulla oblongata ; which, with thefe Ad- ditions, fotms the Corpora -'Pyramidalianni Olharia, and is extended into the Spinal Marrow. And from the fame Medullary Subllance, both in the Cranium, and in the Cafe

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A

form'd by the Union of the Vertebra, arife all the Nerves, See Nerves; lee alfo Corpora 'Ryramtdalia.

Tho the primary Flbrilld, or Filaments, when united, feem to form one compact Body or Mafs : yet Boerbaave Ihcws, they arc really dillincf and feparare from each other- that thus arifing from each Part of the Cortex, and tending as it wete to the Centre of the Sphere, they firil form the Medulla ; that others, reflected hence and collected above form the Corpus Callofum and Fornix ; and below, form the Corpus Callofum snA Legs of the Medulla oblongata ; that the like Fibrillie arifing from the Cerebellum, join with 'em: the Refult of which Juncture, is the Medulla Spinalis. And laltly, that the like Flbrilla arifing from the Cortex, continued within the Cavities of the Medulla, join with 'em, and add frefli Confidence thereto.

Hence we fee the Reafon of the Bulk, Figure, and Po- fition of the Cortex of the Brain, as well as the Ufe and Neceffity of the Cavities cali'd Ventricles of the Brain: Of thefe Ventricles there are four, one in each Hemi- fpherc ; feparated by a thin transparent Subllance, running all along from the Fornix under the Corpus Callofum, and dillinguifh'd by the Name of the Septum Lucidttm .- Thefe are cali'd the Lateral Ventricles. The third is un- der the Fornix, and cali'd Rima ; the fourth between the Cerebellum and Medulla oblongata : To thefe arc owing the Callus's or Knots found in various Parts of the Brain i as freffr Acccfuons of Fibres arrive from the fevcral Places to the Cerebellum.

From the whole, it appears pad doubt, that the Fibres of the Brain are exceedingly minute Canals; that they re- ceive an Humor, infinitely the moll fubtile, fluid, moveable and folid of any in the whole Body ; prepar'd and tecrcted by the artful Structure of the Cortex, driven into thefe Tu- bules by the force of the Hearr, and from every Part here- of collected into the Medulla oblongata : And this is what fome call Animal Spirits, others the Nervous Juice; the great Inflrument of Senfation, mufcular Motion, igc. See Spirits, Muscle, Sensation, &c.

In the Space between the two Hemifpheres of the Brain, under the Falx, or rather under the Loazhudinal Sinus of the Dura Mater, is a white Subif.ince,^Sfa Texture mote compact than the refl.of the Medulla of the Brain ; and for that reafon cali'd Corpus Callofum, which runs along the whole Tract of the Falx, and receives from each fide the Terminations of the Medulla, intcrfpers'd between the feveral Windings of the Cortex, and fuppos'd by fome to be a kind of Bafe ot Support to it : The manner wherein this is form'd, k fhewn above. We /hall only add, rhaton occafion hereof, fome Authors, M. Jftruc for Inllance, in- flead of two Subllances, vis. the Cortex and Medulla, di- vide the Brain into three ; viz. the Uppermoll, or Cine- ritious, which conflitutes the Cortex ; the Middle, which is whiter and denier than the firfl, and therefore cali'd the Callous ; and the Lowell or Inmofr, which being inter- mix'd with Radii or Stria of the White and Cineritious Subllance, he calls the Striated Tart : He adds, that the Fluid (ecreted in the Cottex, is convey'd into innumerable minute hollow Medullary Fibrillin, of the fame nature with the Cahous Subllance, and contiguous thereto. This mid- dle, or callous Part, he obferves, is not diflingui/li'd by any appearance of Fibres, but is uniform, homogeneous, elaf- tick.and not unlike the Pith of the Eldar Tree: for which Reafon, he thinks it a probabie Conjecture, that it confiils of innumerable Cells, communicaring wirh each other, di- vided by the Interpofition of membranaceous, flexil, 'elaf- tick, vibratile Parietes or Columns ; which being flow'd over by the Spirits, and continually expos'd to the Shakings thereof, conflirute the Fibres of the Brain.

Now the fecreted Fluid flowing equally from each Point of rhe Cineritious Subflance into the Callous, mull equa- bly fill and dillend the Cells thereof: And left any Place fliould want its fhare, Provifion is made for a flrift Com- munication ; not only by the Apertures of the Cells into each other, but alfo by the Struflure of the Brain ; the uppct Parts communicating with the under, by the Septum Lncidum; the Lateral with the Lateral, by the Lata Com- mifjura ; lallly, the fore Parts by the hind Parts, by the Crura, Brachia, and Roots of the Fornix. Thefe Cells, he continues, being fill'd, the Spirits will proceed to the contiguous Stria of the Medullary Subflance; which ari- fing "from the Cortex, compofe the Striated Part of the Brain : And thefe Stria render'd narrower and ilenderer, and pairing without the Surface of the Brain conftitute the fid! Principles of the Nerves, (gc.

The other Parts of the Brain, are the Fornix, a Produc- tion of the Medulla ; wlrich, at its Extremity next the Ce- rebellum, fends out two Procefics or Legs, by whofe Junc- ture is form'd a kind or' Arch, thence cail'd Fornix, which feparates the third Ventricle from the two upper ones : At the Bottom of the Fornix are two Holes, by which the third Ventricle has a Communication with the others ; rhat before is cali'd Vulva, and that behind Juus. The third

Venrricie,