Page:Cyclopaedia, Chambers - Volume 2.djvu/174

 MEL

( W )

MEM

The Subftance of the Medulla Oblongata being only an Aggregate of thofe of the Brain and Cerebellum, mull, like them, be purely fibrous or nervous, and only an Af- ierriblage of minute Tubes for the Conveyance of the A- nimal Spirits. It arifes, as it were, from four Roots; whereof the two largeft fpring from the Brain, and arc call'd Crura: the two letter from the Cerebellum, which Dr, Willis calls Tedunculi. See Brain, Cerebellum.

There are feveral Parts or Members of the Medulla Ob- longata, particular Defcriptions whereof will be found un- der their proper Heads. In the general it may be ob- ferv'd, that, upon inverting ir, the firft thing that appears japon its Trunk, is a Protuberance fomewhat like a Ring, for that reafon call'd Protuberant^ Annularis. Then fol- low ten Pair of Nerves, which have their Origin here, ■and arc hence fent to the feveral Parts of the Body. See Nerve. Immediately under the firlt Pair, or Olfac- tories, appear two fmall Arteries, or Branches of the Ca- rotides. The fecond Pair, or Optics, being cut off, ap- pears the Infundibulum, which ends in the Glandula Pituita- ria, and on each Side, the Carotid Arteries enter the Skull j In the Lateral Ventricles of the Medulla arc two Promi- nences on each Side, the one Pair call'd Corpora Striata, from the appearance of Stripes, or nervous Fibres, within them j their outer Subftance being cortical or glandulous, like the reft of the Surface of the Brain, tho' not fo deep. Betwixt the Corpora Striata is a broad thin Production of the Medulla, call'd fornix ; and underneath them lie two other Prominences, call'd Thalami Nervorum Opticorum, On either fide of thefe is a Plexus of Blood-Veffels, cal- led Plexus Coroides. And under the Fornix a narrow Aper- ture, call'd the Rima, which lets into the Inftmdibulum ; which is a Paffage from the third Ventricle to the Glandula Pituitaria, thro the Medulla of the Brain ; being lined with the Fia Mater. Under this, in the Sinus call'd Sella Equina, or Turcica, upon the Os Cribrofum, is the Glandula Pituitaria 5 which is furrounded with a Plexus of Veffels, call'd Rete Mirabilf, only vifible in Brutes. On the hind part of the third Ventricle is a fmall Foramen, call'd Anus, leading to the fourth Ventricle of the Cerebellum : At the Orifice of this is feated a fmall Gland, which, from its fancied Re- femblance to a Pine Apple, is call'd Conariutrf, or Glandula Pinealis ; where Des Cartes and his Followers imagine the Seat of the Soul to be. On the backfide of the Medulla Oblongata, near the Cerebellum, are four Protuberances, whereof the upper and larger are call'd Nates j the under and lefTer Tejlcs. Between thefe and the Procefles of the Cerebellum, is the fourth Ventricle, from its Figure call'd Calamus Serif tortus. On the Medulla Oblongata, near its Ex- tremity, are four other Prominences, two on each Side 5 call'd Corpora Pyramidal'ta and Olharia. See Pyramida- zi A, Olivari A, Calamus, Conar ium, Rete, &c.

Medulla Spinalis, or the Spinal Marrow, is aContinua- tion of the Medulla Oblongata, or Medullary Part of the Brain, without the Skull. It confifts, as the Brain does, of two Parts, a White or Medullary, and a Cineritious or Glandulous ; the former without, and the other within. The Subftance of the exterior Part is much the fame with that of the Corpus Calloftim, only fomewhat tougher, and more fibrous : which Difference becomes the more apparent, as it defcends the lower ; by reafon of the Streightnefs of the Cavity, which growing gradually more narrow, prefles the Medullary Fibres clofer together, and renders them more compact, and gathers them into more diftincl Fafciculi, till having defcended the whole Tra<fl of the Spina, they end in the Cauda Equina. It is the Origin of moll of the Nerves of the Trunk of the Body : It fends out thirty Pair on each Side to the Limbs, the great Ca- vities, and other Parts; which are nothing but Fafciculi of Medidlary Fibres, cover'd with their proper Membranes. See Nerve.

The Spinal Marrow is generally faid to be cover'd with four Coats : The firft, or external one, is a ftrong nervous Ligament, which ties the Vertebra; together, to the Infide of which it firmly adheres. The fecond is a Production of the Dura Mater ; it is exceedingly ftrong, and ferves to defend the Spinal, Marrow from any Hurt from the Flex- ures of the Vertebra:. The third is a Production of the Arytcenoides, and is a thin pellucid Membrane, lying be- tween the Dura and Fia Mater, or the fecond and fourth Membranes of the Medulla. This Membrane gives a Coat to the Nerves, that go out of the Spina, which is the inner Membrane of the Nerves, as the Dura Mater gives the outer. The fourth Coat is a Continuation of the Pia Ma- ter, and is an extremely thin, fine, tranfparent Membrane ; ftriclly embracing the whole Subftance of the Medulla, dividing it in the middle into two Trails, and making, as it were, two Columns of it. See Spine, Vertebrje,

Medulla 0^b;«, or Marrovj of the Bones, is a {oft fatty Subftance, placed in the Cavities or Fores of divers Bones j it is inclofed in a Membrane j and is devoid of Scnfe : it

is red in the greater Cavities, white in the lefs, and foil and fucculent in fpungy Bones. See Bone. From this is fecreted the Medullary Oil. See Medullary Oil. , MEDULLARY Oil, is no more than the finer and more lubtile larts of the Medulla, or Marrow of the Bones fo call'd. TBis, Dr. Haven obferves, paffes not into the Bones thro Duffs, but by fmall Fores formed into the Veflels or Glandules, which are conglomerated into di- ftmS Lobules, contained in feveral Membranes invefling the whole Marrow ; all which Veficles or Bags are pro- pagated from the outward Coat of the Arteries; and by thefe it paffes from one to another, till it arrives at tha Sides, or extreme Parts of the Bone. That Part of it which is fupply'd to the Interfaces of the Joints, goes into them by Paffages, penetrating thro the Bone into thofe Cavities, and form'd ior that end. The Ufe of this Oil is either common to all the Bones, whofe Temper it pre- ferves, and keeps from being too brittle ; or more pecu- liar for the Joints, where it is very ferviceable, (i./To lubricate the Bones at their Extremities, that they may move more eafily and free, (..) To keep the Ends of the articulated Bones from growing hot with Motion. (3.) To pteferve the Joints from wearing by Attrition, and rubbing one againft another : And, C4-J To pteferve the Ligaments of the Joints from Drynefs and Rigidity ; and lubricate thofe Farts, which Aide upon the Bones, and keep the Cartilages, which are join'd to them, flexible.

MEETER. See Metre.

MEGALESIA, in Antiquity, a folemn Feaft celebrated among the Roman; on the nth of April, in honour of the great Mother of the Gods, that is, Cybele or Rhea ■ wherein, were Games or Combats held before the Tem- ple of that Goddefs. They were call'd Megnlefia, from the Greek {j.;~,a>.«, Great; Cybele being accounted the great Goddefs.

MELA, a Chirurgeon's Inftrument, call'd lift) Speculum and by the Vulgar, Tenta. Its Ufe is to probe Ulcers' draw a Stone out of the Yard : Its Form is various, ac- cording to the Ufes it is intended for. See Speculum

MELANAGOGUES, are fuch Medicines as are fup- pos'd particularly to purge off black Choler; from ,,k«j niger, black ; and i-p, duco, to lead : but there is no fuch Ditfincfion of Choler now regarded, and confequent- ly this Diftinction is but little ufed. See Purgatives.

MELANCHOLY, in Medicine, the Name of a Dif- eafe, which confifls in a Delirium, without a Fever, and is ufually attended with Fear, Heavinefs and Sor- row, without any apparent Occafion. The Antients attri- buted this Difeafe to black and cloudy Spirits, arifing as Vapours from a redundant black Bile. Some of the Mo- derns afcribe it to the irregular Motion of the Spirits, and their acid Conflitution ; and others, who know it better, to too heavy and vifcid a Blood, which permits not a Sufficiency of Spirits to be feparated in the Brain, to ani- mate and invigorate the Nerves and Mufcles: And others to a Drynefs of the Meninges of the Brain. This Difeafe is vary'd an infinite number of Ways, according to the Temperament and Ideas of the Perfon affected with it. It is a Species of Madnefs, and only differs from a down- right Mania in degtee. The Word comes from the Greek hsa«, niger; and %m, Bile. See Madness Delirium

MELCHISADECHIANS, antient Sectaries, fo call'd, becaufe they rais'd Melchifadech above all Creatures, and even above Jefus Chriil. The Author of this Secf was one Theodotus ; whence the Melchifadcchians became more commonly known by the Name of" Theodotians i all the Difference between thofe, and the Uriel Theodotians, con- fitting in that patticular Article relating to Melchifadech t who, according to them, was the great and fupreme Vir- tue. See Theodotians.

MELCHITES, the Name of a Religious Sefl in the Levant, who fcarce differ from the Greeks in any thing re- lating either to Faith or Worfhip ; but yet fpeak a diffe- rent Language. The Word, in the Syriac, fignifies Roy- alijts, and was formerly apply'd to the Catholics by the Heretics, who refus'd to fubmit to the Decifions of the Council of Calcedon : intimating by this Appellation, that they were of the Religion of the Emperor. Thofe now call'd Melchites, are fuch People, as, inhabiting among the the Syrians, Ccphta; or Egyptians, and other Levantine Na- tions, follow the Opinions of the Greeks, tho no Greeks them- felves : And 'tis for this reafon that Gabriel Sionita calls them indifferently by the Name of Greeks and Melchites. The fame Author obferves, that they are fprcad thro* all the Levant ; that they deny Purgatory ; and are declar'd Enemies to the Pope and his Primacy. For the reff, they fall in with the Greeks, both as to Articles of Faith and Difcipline. They have tranflated the Greek Euchologue, and other Books of that kind, into Arabic; and have the Canons of Councils in the fame Language. To thofe of the Council of Nice, they have added new Canons, com- monly