The economy of the animal kingdom, considered anatomically, physically, and philosophically

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vascular, like the first tunic of the artery. The third is glandular, lihe the second of the artery. The fourth and inmost tunic, like thothird tunic of the artery, consisis os annular sibres, but thinner, and ar-ranged in a Very Simple SerieS. . . .

The vena portae has thicher coatS, SO as to appear in a measure tobo an intermediate between the Other VeinS and the RrterieS. . . . The velias are much larger aud more capacious than the arteries.. . . ΝeVeriheleSS a much greater quantity of blood flows through the arteries than through the vetus, is you excepi that part of the vena cava that lies between the insertion os the thoracic orJ chylii erous duet, and the right ventricle of the heart. In dead subjecis almost allthe blood is found collected in the vetus, While the arteries are usuallyempsy. . . . In the cavlty of the Velias, at disserent intervais, there are certain very thin, light pellicles, called valves, Whicli at One extremity, namely, toWard the Sinalter tWigs, are continuous With the interior Venous coat, While at the other, namely, toward the heari, theiredgeS Rre free. . . . They are frequently sound near the divisions of the velias, or the junction of the branches ; and somelimes are Single, Sometimes in patrs, somelimes in tripleis, yc. The lalter are placedanteriorly and posteriorly With respect to the body, While the former or the single have a lateres position; or vice vel δα. Corp. Hum. Mai., lib. i., tr. i., cap. iv., p. 13 - 15 ; BruXeli., l7l0.) Is the crural vesseis be exposed and lied, for instance, in a livingdog,) the vein s elis up in iis narrower pari, that is to Say, On the Sideos the ligature farthost froin the beari, while the part that is broaderand nearest to the heari collapses. The contra happens With the

As it is the office of the venous tWigs to receive the blood fromthe litile arteries, so Ne sud that these two seis of veSSeis constantlyetther accompany or meet each other: but the larger venous branchesare somelimes bound up With the arteries, and Sometimes separate fromthem; and indoed not urifrequently the vetus mount up Over the arte

nected Mith each other, but also blood-vesseis of the fame Liud; frequently, that is to say, vetiis With vetus, and arteries With arteries; so much So, indeed, that there are scareely any considerable tWigS run- ning from the fame trunk to the fame region, but aster their division again unite, at any rate by minute anastomoses. Most anatomisis havehitherio considered such anastomoses to be confined to the regions os the head and uterus ; . . . but they are beautifully seen externalty in the si in of a foetus of six or seven monilis. Ibid. , p. l2, I 3.) The circulatory motion or circulation of the bl ood is as sollows.

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Τhe bl 00d passes from the trunk of the vena cava, and si Om certain Ofits branches, into the right ventricle of the heari, in part immediately, in part mediately through the right auricle. Froin the right ventricle itis expelled by the contraction of the listari into the pulmonary artery, by the litile branches of whicli, distributed through the lungs, it is con-Veyed tuto the twigs of the pulmonary vein, and passes along the trunk of this vein to the lest cavlty of the heari, in part immediately, and inpari mediately through the lest auricle. From the lest ventricle it is expelled by the contraction of the heari into the aorta, and by the ramifications of this vesset is distributed ali over the body. That portion os the blood that is notther converted into solid Substance, norinto any Other matter extraneous to the circulation, passes frOm thelitile branches of the aorta into the litile branches of the vetus, and attengili comes bach through the trunk of the vena cava to the right

ventriole of the heari, si Om Whicli it Started. . . .

Is an artery of a dog be tied, and punctured With a lancet above the ligature on the fide nexi the heari, provided the animal be healthy, tho blood will spiri out in a strong j et to the height of severat cubiis ;and is the artery be lest open for any tength of time, the dog Willdie from loss of blo d. Is however the puncture be made On theother fide of the ligature, very litile is any blood Will escape. Butis a Velia be punctured, the contrary Will happen: on the si de of the ligature nexi the lidari no blood Will escape, While on the other fide a copiolas stream Will be emitted, although not With such force as When

large vesseis than through the smali. To demonstrate this positionhe constructed tWo iubes, and made them communicate With each other by means of Amalter iubes, so that ali together formed a continuous

pipe. Ηe does, in faci, prove that the liquid sent through one of the larger iubes moves mitti equat rapidi ty through the other. WithreSpeet to the smaller iubes, it is evident, that unless collectively theyare os a calibre not inferior to that of the largor iube, the liquid mustruit through them more rapidly than through the larger. . . . The SamemOSt curious inquirer Walched through a microscope the circulation of

of one hour, it amounted to a distance of 288 inches . . . Or 24 seel. . . . Fr0m thiSJ he concludes, that in a mala, the bl od circulates froni the heari to the extremities of the Dei and bach again, only tWice and tWo thirds in an hour. And that in the fame time it completes fourtimes and a litile more than one third of the whole circle, through the

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spirat fibres, the spirat fascioles being superimposed One Upon another, and connected together by means of vilicus fibriis. The interior tunicis shewn to be made up of flat membranous expansions, lying Straightalong the artery. In representing the tunics of the vetus, he delinealestheir outermost fibres as irregularly longitudinat, tensile and tendinous, attached by their extremities to certain fleshy tubercles, and to certain longitudines lines of the fame substance. He depicis the nexi tunic of the

as having innumerable glands attached to, and set iii, it; Whicli glandsare connected together by litile fibres and vesseis, that by their multitude

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by artificiat injections os prepared wax, such as are made by the celebrated Rub sch. The second tunic Was sirst discovered by thiS anatomist, Who described ii as a cellular coat, partining entirely as it does of the character of that subculaneous cellular membrane that is disrused throughout the body, and whicli, togother With the sat ericiosed in iis celis, is generalty enumerated among the universat integumentS, under the Specific name of panniculus adiposus. In the large arteries near theheari, this membrane perceptibly takes up a salty juice emulged froni the blood-vesseis of the superincumbent tunic, and diffuses it, though

a litile of salty matter. The celis of this tunic may be shewn either by inflation or by the Ruyschian modo os injection. The third tunicis termed by Willis, glandular, as being made up of innumerable minute

White glands closely cro ded together. These gland S discliarge a mu-cilaginous humor, whicli together With the salty juice above mentioned, must in no sinali degrest facilitate the motion of the undeHying mus- Cular tunie. . . . The fourth tunic is properly called muscular, Since it consisis entirely of two layers of muscular fibres ; that is to say, a circular or spirat, and a longitudinal layer ; their tendinous and nervous expansions being observabie Within. The motion of the arteries is carried on solely by means of this membrane ; the spirat fibres compresSing and constricting the vesset, and the longitudinat elevating and dilating it, much in the fame manner . . . as in the intestines. Willisadds to the foregoing another tunio, Which he calis nervous. But this tunic is not distinet either in substance, nature, Or ossice, froin themuscular tunic, but is composed entirely of iis longitudinal fibres audiendinous and nervolis eXpansious intertWined, and there re we Shallitot malle it the subject os a separate description. We Will here mention only, that the strength of the artery is derived entirely froni themuscular coat, and that is this coat be lacerated, cui, or dilated by any force, externat Or internat, an expansion of the artery, or ananeurism, is the result; for the intrinsic sos iness of ali the other tunics causes them to yield at onoe to the pulsations of the bl od. Theatr. Auret. , tom. i., p. 192, 193; sol ., Gen., 17l6.) The vetiis have the Same tunios as we have described in the arteries, but they are muchthinner, and the cellular tunio, is it be not altogether Wanting in them, Dan at any rate hardly be demonstrated. Moreover the muscular tuniri Whicli in the arteries is a single structure compoSed of tWo SetS Ororders of fibres, sortias in the vetus tWο membranes. Thus the longitudinal sibres that in an artery forni the inuer order immediately Under-lying the spirat fibres, form in the vetia a peculiar tunic, inveSting it

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existriorly, and whicli, theres ore, is Separated frona the spirat fibros, whicli are siluated more in Wardly, by means of interpOSing membra es, vascular and glandular. But ali the venous tunios are comparatively

nothing of the number of the tunics, on Whicli subjeci I have no Wishto dispute. I observe, that sonae things Which you and Verheyen aSSertrespecting the characteristies of these tunies, I have no difficulty os recogni ging in the arteries of oxen ; but Whether they can be shewn bysufficient evidelice to hold good in those of the humari subject, I have my doubtS. . . . Mucii more do I doubi . . . Whether the fleshy fibres in the tunios of the arteries are spirat and longitudinat,' and serve thepurpose of elevating and dilating the artery, as in the intestines; justas it there vere no other circumstances to be taken into account in the arteries, and as is ample reason for their elevation and dilatation wero

not to be found in the intrusion and forcibie propulsion of the blo d. And for my pari, not only do I not aclino ledge that there are any sufficiently manifest longitudinal fibres in the internat coat of the arteries, but supposing that there are none, Ι thinii I see how it is that others have sumetimes sancied they could discern them. In fine, Ι observe in the arteries no fleshy fibres at ali, except Such as are annular; nor do I

and Verheyen delineate any others. Adver8uria Anatomica ii., Anim. 38.) That the vena cava in the larger animais, that is to say, both in man and brutes, at iis ingress into the heari, is entirely muscular,' will not eastly be admitted by one Who has seen the vena cava of the Oxindeed, provided With a red and poWersul muscle analogous to a Well-marhed sphincter, but has fought in vain sor a like muscle in the humari vena cava; although Ι Would not for this reason deny to thelalter a muscular character and poWer.'' Ibid. v., Anim. 15.)

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branches. 2. The figure of the arteries is conoid, running from alarge diameter to a smaller. In the extremities of the body, hoWever, the tWigs become cylindrical cannis, and terminate somelimes in reticular plexuSes, somelimes in litile bruShes, spirais, glomes, &c. ; and attength in Serous Vesseis, vetus, lymphatios, or excretory ducis. 3. Τhenrteries are of a membranous structure, being made Up of sive coatS,

the first of whicli is vascular, the seconii cellular, the third tendinouS, the solarili muscular consisting of a vast number of annular fibres), and the fifth nervous. Comp. Anat. , D. 29l.) For I finit . . . that sive costis at least may be rectioned in the arteries, ali of whieli are very distinet and manis est in the larger arteries, and particularly in the trunk

The second coat consists of numerous retisorin plexuses, and is divisibie into severat layers, Whicli nevertheless, aS being homogeneous in sub- Stanee, I have considered Only as One coat . . . . The third coat is a firmand tough membrane, almost Of a tendinous character. When this Oat is removed, We come to a dense and thicli iunio made up of a vastnumber of plain muscular fibres, surrounding the arteries like a circleor ring, and Whicli tunic, by reason Of iis thichness, is also readilydivisibie into severat layers. . . . Lastly, there is the fifth or internalc0at, underlying the fleshy annular fibres, and termed the nervous coat. . . . I am ut a loss to know the reason f r Whicli Some anatomisis Venture to deny to the arteries the possession Os a muscular coat, and of the requisites of muscle, whicli requisites consist iu a visibie fibrous substance, and in the poWer Os contraction and the exercise of motion ;)sor the annular fleshy fibres in the arteries are sar more manifest and of

sar greater thichness than in the intestines , and constitute various sufficiently rema rhable reddish layers, fas I can SheW to any one anyday he pleases,) and in propelling the blood, exert a much more plain and soroible constrictile action aud motion than the fibres of the intestines exert in propelling the food . Νor is it true, that muscular Structures are incapable of ossification ; for not to mention the sesamoidbones, Whicli are Often soland here and there both in the origins andinSertions Os Various muscies, the dura mater itself, Whicli in theopinion Os recent anatomisis is muscula ) and the very intestines, in both of Which bony substance is occasionalty detected, sufficiently dis-pr0Ve the poSition. Ibid. , not. 63.) The vetiis are compoSed of a

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ΤHE ARTERIES AND VEIN S.

thinner than in the arteries. In some of the branches of the vena cava there are semiiunar valves, Whicli assist in the circulation of the blood ;but there are no valves in the vena portae, nor in the pulmonary Velia. Ibid., n. 298.) The vena cava commences by a large sinus froin theright auricle of the heart, . . . and divides into tWO trianks, a Superiorand an inferior. The Superior trunk is siluated on the right fide, and

j Ugular Vein, . . . the internat jugular Vein, . . . the Vertebrat Vein, yc. . . . The inserior trunk is rem arkable for the Eustachian valve, andrians a Very Short course in the thorax, Scarcely in faci sor three quartersos an inch. Νear the liver it mahes singular inflectioris, Which have passed unnoticed by recent anatomisis, although delinealed by Vesalius, and stili beller, as Morgagni insortiis iis, by Eustachius, in his Tabul. Anai., tab. XXV. From this trunk proceed the diaphragmatic or inferior

phrenie VeinS, . . . the hepatie VeinS, . . . the renes Vein S, . . . the right

Spermatic Vein, . . . the illac Veius, yc. Ibid., D. 296.) As to the Eustachian valve, ... I find that Cheseiden made the sirst mention osit, in the first edition of his Anatomy, p. 90, London, l7l3. . . . Hea scribes the discovery Os it to Dougias . . . . It is probable that tab. viii. , fg. Vi., in Eustachius, OFu3cula Anatomica, sirst published at Venice in 1564, . . . gme DOUgias the hint for this . . . . But Eustachius does notcali it a valve, but a membrane of WOnderi ut construction, placed be- fore the molith of the vena cava ascending froin the liver, just Where it begitis to merge in the right auricle, occupying iis anterior half, and forming a Lind of reticulation.' . . . Lancisi thinks . . . that thiS Valve prevenis the blood descending from the jugulars through the superior caVa, from encountering too violently the blood ascending through tho inferior cava. But Winslow is the author Who has best os ali described this valve, and explained iis nature. He calis it the reticulatest valve os Eustachius, and has given an elegant figure Of it lunated and reticulated, and described iis siluation and connection much more accuratelythan any body who had gone bes ore hi m. He observes that iis concave part is turned upWard, and iis convex part doWnWard; and ShewS,moreoveri that in looking for it in dissectioris, the posterior part of thecaVa, not the anterior, is to be opened ; otherWise the valve Will noteastly be found . He observes that it is very frequently absent in adulis,in whom the foramen ovale is closed; and is best Seen and demon- Strated in very young insanis particularly, and in other subjecis in Whomilie foramen Ovale is operi: and ali the better is the paris be placed in a VeSSel of Water. . . . He She s that it not only has the use that Lancisi

assigris to it, but especialty in the scelus at birth, Where it is most ob-

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domen. Τhis arcti, from the base of the heari to the place Where it begius to descend, according to Morgagni, is about Seven finger-breaditis long ; and from the potnt Where it begitis to descend, it is called the descending trunk of the aorta, from Whicli are derived allthe arteries of the lower paris of the body. Froin the upper part of the arch, in the human subjeci, most commonly three large branches ascend ; the right branch then divides, more or less remotely froni thetrunk, into the right subclavian and right carotid artery; the middie constitutes the lest carotid; and the third the lest subclavian Sometimes, although rarely, I have found Dur ascending branches in the feniale ; the tWo outermost forming the tWo Subclaxian arteries, and the two middie, the two carotid arteries. I have in SpiritS a preparation injected With Wax, shewing this variety.) But it is very rarely, is ever, that there are Only tWO aScending branches in the human subjeci, much less do we find Only one ; and lience the storta cannot be dividedinto an ascending and descending trunk. But in dogs, calves, and various Other beaStS, Only one large ascending branch is generalty observed, and frOm this circumstance the error mentioned above appears to have arisen : although even this Single branch has commonly asinali branch running beside it . . . . The branch that constitutes thelest carotid, generalty comes Osf by a persectly distinet origin nearly in the middie belween the sirsi and third branches. . . . That the right carotid arises froni the subclavian, is a fact Whicli I most olearly recognigo both in Draho's figure in his Anthropolos., tab. XX. , and in the explanation he gives of it. Ibid., not. 64.)

may take any branch we please ; but in order to render the experiment more palpabie to the naked eye, let the great artery be Selected, and having fit ted into it a cylindrical piece of wood, let the artery be frequently Wetted with hot water : then With the knise and probe let usproceed by degrees froni the externat paris to the interior ; and we Shail find by this means that the arteries are composed os four distinctmembranes. The si si is purely vilious, and consists of extremely sne sitamenis, Whicli is Me attempt to raise we Shali See inter Oven Mith

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these stamenis there is a complicated tissue Os extremely stender ves-self, both Sanguineous and nervous. We nexi meet With a secondinembrane os a denser structure and more resisting. This membraneis thought by Willis to be glandular, and to me appears to be as it Were a propagation frona the pleura or interior membrane of the peri- cardium ; for it has a similar solidity and texture, and is likewise provided With numerous longitudines fibres. The third membrane at which we arrive is plainly fibrous, and is the thichest of ali; so muchso indoed, that With a litile dexteri ty and patience it may be separated

particularly deseruing of notice, the fibres of this coat, whicli are likoned by Galen to the sineWy fibres flacerti of the stomach, are in reality uot of one but of many orders, sor the m0Si part being spirat, that is to say, running obliquety in a gyre ; Whicli circumstance has

caused sorne authors to asseri that this membrane consists of circularand tra SVerse fibres . . . . The fourth or last is the finest of ali themembranes, but strong, and although it contains Only the most minutes ramina, is nevertheleSS transparent, and may be Seen through Whenheld up to the light. This coat of the arteries corresponds to that Whicli lines the inside of the ventricies of the listari, and whicli belligmade up of a most dense tissue Os villi, alone confines the more subtile and volatile particles of the blood , Which would otherWise no doubtin great pari malle their escape ; sor the looser texture of the other membranes could hardly avail to Leep them in . In this membranethere are two other things to be noticed. In the sirst place, iis inner

the blood is rendered more rapid, and the way lubricated. In thesecond place, What we do not meet With eVeryWhere, but only in certain paris, and chiesty in the large branches of the arteries,) We finda distribution os certain adipose follicles, Whicli are clearly seen in thenoria Without the microscope, and by Whicli it is probabio the sat is secreted and collected, and aster artis at the proper seaSonS graduallythrown Out here and there, in Order that the arteries may thus be kept lubricated with an Oily substance of the kind, as We said above. De Motu Cordis, &c., lib. it., cap. it., Prop. Vi.)122. VI EUASΕΝΗ. The arteries are provided With four coats, namely, With One common coat, Whicli they put Osr When they enter into the interiors of paris ; and With three proper costis, the middie of Whicli consists of annular fibres, sume hat hard and resisting. The sarther the arteries are froin the heari, the Smaller they are, and the

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narro er in calibre. . . . It is very evident that in that motion of the arteries Whicli is properly callod dilatation, their costis are stretched in every direction beyond their natural degroe of tension. Some hmethought With Galen, that this extension depends upon a pulsisic lacully; and others With Millis, that it depends upon the animal spirit. We cannot however but agrest With those who maintain that the arteries are dilated by the blood. For as the blood in iis exit froin the heari, traveis froin the larger to the lesser arteries, on iis Way to the remoterpartS, it must necessarily communicate iis entire nisus to the parieteSof these h0llow pipes, and by means of iis expansive motion, and of the impulse superadded to it by the contraction of the heari, OVercomethe resistatice of the fibres of whicli the arteries consist, and in the Same proportion dilate them. In this opinion We are confirmed by the folloWing eXperiments, Which were made With the greatest care in the

Water a number of smali iubes, of disserent tength and calibre. In the Secund place, We fastened a dog to a table, laid open iis abdomen, and lied iis mammary and epigastric arteries; and laid iis test hidney, Spleen, Stomach, and intestines, back on the right fide. The superior