MAR
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whereas the other is more folid, and is only red on its furface. This difference is owing to the blood-veffels which run thro' each membranous cell, whereas the Marrow in the great ca- vities Teems to he furnifhed with them in the common mem- brane only. Many of thofe medullary cells are likewife di- vided by the bony filaments of the cavernous fubftance; and thefe fmall filaments, as well as thofe of the reticular texture, are covered by portions of the medullary membrane, as by a periofteum.
The medullary membranes may be feparated from the liquor which they contain, by fteeping the whole mafs in very hot water, and afterwards comprefling it by gentle degrees. But it is to both thefe fubftances, taken together, that the ana- tomifts give the common name of Marrow, not to either of them taken nngly. The medullary membrane is very fenft- ble, but not the juice, which is neceffary to be obferved, to underftand properly what is meant by the fenfibility of the Marrow. The Marrow, by its liquid and unctuous part, renders the bones in fome meafure pliable, and lefs brittle, as it continually pervades their fubftance in fmall degrees : This continues to old age, and then the bones; being deprived of their Marrow, become very brittle.
In the bones of the oiTa innominata, there are no internal large cavities ; but their fubftance being ccllulous or caver- nous, they contain no medullary mafs, but their cells are all moiftened with a medullary juice, which diftils inceflantly through the membrane with which they are lined. In the os femefris the marrow lies in a large mafs, in the middle cavity of the bone, and in fmall diftinct clufters in the cells of each extremity. The firft is penetrated at different diftances by tire bony filaments, and is thereby fuftained in all violent motions and fhocks, as running, leaping, and the like. In the bones of the leg the difpofition is exactly the fame ; and in the bones of the foot, the Marrozu is fuitable to their internal ftructure, and is lodged in molecular, in the cavernous portions, and in maffes in thofe which have cavities to receive them. Thus the Marrozu of ail the tarfal bones is difperfed in moleculse, becaufe their internal ftructure is fpongy. In the metatarfal bones, and firft phalanges of the toes, it is difpofed in the fame manner as in the tibia and fibula, that is, it lies in mole- cular in the extremities, and in their middles in greater or leffer maffes, according to the fizes of the cavities. In the other phalanges, which are entirely fpongy, it is accordingly dif- pofed in molcculse. In the vertebrae, fternum, and ribs* the internal ftructure of all which is cellular and fpongy, the Marrow is contained only in fmall feparate portions, and is no other than a red medullary juice. The bones of the head alfo being in like manner cellular in their internal ftructure, contain alfo their Marrow, in like manner, in diftinct por- tions, and lying in membranous ceils in the diploe. Wirt- Jlcw's Anatomy, p. 118, 136, 150, 152. The tranfpiration of the unctuous matter of the Marrow is not confined to the time of the animal's life, it is even carried on in the dead carcafs, and is one great obftacle to the whiten- ing and cleaning the bones in a fkeleton ; for if there be not an opening made at one end of a bone, and the Marrow waffled out of the whole bone at this aperture, by means of proper liquors injected with a fyringe, the bone, though made ever fo white at firft, will certainly turn yellow after- wards, by this tranfpiration of the Marrow contained within it, which certainly happens on the lead heat of the weather, or ofherwife. For this reafon it is alfo, that the workmen who ufe bones always cut them longitudinally in two, and take out all the Marrow, and even all the fpongy fubftance of the bone, which might be fuppofed to contain it, otherwife they know that the heat of any one's hand will turn their works yellow, tho' ever fo white when firft made. It is to be obferved, that there are in the hollow bones feveral fmall aper- tures thro' which there pafs blood-veffels, which go from the membrane enclofmg the Marrow ; whence it appears that the bones are indeed nourifhed from within as well as from with- out, though that be not by the Marrow, but by the blood- veffels only : Thus the two tables of the fkull are evidently nourifhed ; the external one by the veffels of the pericranium, and the interior by the branches of thofe veffels which are fpread along the dura mater.
It has been fuppofed that the quantity of Marrow increafed in the bones according the increafe of the moon ; but this has been found a wholly erroneous opinion, the increafe of the Marrow in all the bones depending on the quantity of nou- rishment and the ftate of reft which the creature is allowed. 1 he fcnfation of the Marrow has been a point very varioufly ipoken of. When a limb has been taken off, and the Marrow is left bare, if any thing touch it roughly, the patient feels an exquiutc pain. Some had fuppofed that this fenfation might rather ar.fe from the membranes, than from the fubftance of toe Marrowy This, however, was put beyond all doubt by a S *°.. v ? r >' cniel Ration, performed before the Paris
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other part whatever, and the creature, on this, expreiTcd as violent afcnlation of pain as from any of the former opera- tions : This was repeated feveral times, and always with the lame event ; fo that it is very evident that the Marrow is iri its natural ftate, highly fenfible of pain ; and how much more may it be fo in difiempered bodies ! Mem. Acad Par 1700.
The antients fuppofed that the Marrow ferved for the nou- rilhment of the bones ; and their reafons for believing it were that they faw no blood-veffels enter the fubftance of the bones,' by which they could be nourifhed, all the veffels of that kind; which they could difcover, going direflly into their cavities, where the blood they contained fecmed to undergo a fort of concoction; which converted it into Marrow, and by that means rendered it fit nutriment for the bones ; and they ob- ferved, in proof of this, that the longer any bone was, and the more violent ufes it was intended for, the larger was its ca- vity for the containing this nutritious matter. Thefe reafons, though they carry a great fhew of probability, yet are eafily refuted by accurate obfervation. We fee, in young fubjects, a vaft number of blood-veffels diftributed thro' the fubftance of the bones, the texture of which, at that time, is lax and fpongy. It is alfo to be obferved, that there are many bones in the human body, as well as in brutes, which, according to this fyftem, could not be nourifhed at all, fince they contain no Marrow. Of this kind alfo are the horns of deer, and many other creatures, which, tho' they contain no Marrow, yet grow very vigoroufly. There are alfe other bones which are hollow, yet are only cloathed with a glandu- lous membrane ; fuch are the cavities between feveral parts of the two tables of the fkull : And in the elephant, the foliaceous bones, which are in the place of the diploe, contain no Mar- row, and are only covered with a membrane, which has fe- veral blood-veffels fcattered through it. The hollows of thofe bony fubftances alfo which compofe the claws of crabs, lob- fters, and the like, contain no Marrow, but only the muf- cles, whofe office it is to move thofe parts ; and yet all thefe grow, and are nourifhed, as well as thofe bones which con- tain ever fo much Marrow in their cavities. In fine, it may be well concluded, that it is not for the fake of containing Marrow, that the bones are made hollow, but merely that they may be lighter, and more fit for motion. Mem. Acad. Par. 1700.
Obfervation gives abundant proofs, that a great quantity of the Marrow continually tranfpires through the folid fubftance of the bones, and in this action it is of great ufe, though not in the nourifhing, yet in the preferving the bones, its oily and unctuous matter foftening the rigid fibres of which the bone is compofed, and rendering them more fupple, foft, and flexile, and confequently the whole bone much lefs liable to break
MARRUBIASTRTJM, baftard Horehound, in botany, the name of a genus of plants, the characters of which are thefe : The flower confifts of one leaf, and is of the labiated kind! The upper lip is hollowed in the manner of a fpoon, and the lower is lightly divided into three fegments. The piftil arifes from the cup, and is fixed, in the manner of a nail, into thc hinder part of the flower. It is furrounded alfo by four em- bryos, which afterwards become as many feeds of a roundifh fhape, ripening in a fort of open cafe, which was the cup of the flower. There is, befide thefe marks, alfo a peculiar face in the flower of this plant, .by which it is, at fight, diftin- guifhed from the galeopfis.
The fpecies of Marrubiajlrum, enumerated by Mr. Tourne- fort, are thefe: 1. The common Marrubiajlrum, called by fome, the Germander-leav'd Ironwort, or Sideritis. 2. The marfh {linking Marrubiajtrum. 3. The white-flowered fideritis-leav'd MarruUafirwn, with prickly flower-cups. 4. The fideritis-leav'd Marrubiajlrum, with 'prickly cups, and yellow flowers, with edges of a blackifh purple. 5. The motherwort-leav'd Marrubiajlrum. 6. The American Mar- rubiajlrum; with the flowers collefled into heads, and with a fweet fmell like that of baum. 'Town. Inft. p. 196.
MARRUBIUM, Horehound, in botany, the name of a genus of plants, the characters of which are thefe : The flower con- fifts of one leaf, and is of the labiated kind ; the upper lip ftands erect, and is divided into two horns ; the lower is divided into three fegments. The piftil arifes from the cup, and is fixed in the manner of a nail to the hinder part of the flower. It is furrounded by four embryos, which afterwards become four oblong feeds, and are contained in a fort of open capfule, which was before the cup of the flower. Tourn. Inft. p. 102. The fpecies of Horehound, enumerated by authors, are thefe : 1. The common white Horehound. 2. The hairy white Horehound. 3. The broad and roundifh-leav'd exotic Hore- hound. 4. The fhort-leav'd white Horehound. 5. The narrow-leav'd white Horehound. 6. Thc procumbent Spanifh Horehound, with ftellated and prickly flower-cups. 7. The procumbent Spanifh Horehound, with filky and filvery leaves. 8. The ftinking Horehound, as we call it, is the balhte, a different genus of plants ; and the water Horehound, which is the lycopue, is alfo to be feen under its proper head. Marrubium is faid to be an attenuant and refolvent; it is famous for the relief it gives in moiit afthmas, and in all dif-
eafes
