Section IV, (Part 4)

eye. Although the calibre of the vessels decreases in proportion as they are distant from the heart, it is important to state thnt this diminution aifects the branches individually, and not collectively; for it has been ascertained that the aggregate volume oi the branches exceeds that of the trunks from which they proceed. Thus the united capacity of the two common iliac arteries surpasses that of the aorta; and :q^in, the united area of the two subclavian veins is greater thtin tiiat of the superior cava. ■ ' The number of the divisions which occur in thu dif- ■ferent vessels, is liable to considerable variation ; but as Haller and Richat have stated, it seldom happens that any ve.^l offers more tlmn twenty successive division^, from its commencement to iu last ramifications. Each vessel is generally considered to be cylindrical "& fififore, but Mr. Hunter, who performed several ex- periments upon this subject, states that the art«ries are conical, the narrow end of the cone being placed towards the heart ;* we may therefore regard the vas- colar system as representing a cone, not merely in its totality, but also in its indi>idual parts. TTie mode according to which the branches proceed from their trunks, varies in tlie several regions of the body. In some places the vessels bitiircate. and thus terminate in two branches, as in the biiiircatioa of the aorta, of the common iliac artery, of the common caro- Jlm„p,; ' Tiel« oil iho Blood, vol. i. p. 297. 3i6 MOOI Of DlVl»mif . « , t}dt 'k. a sbiQar dbpoaitiafi is oceuiosaOjr o1 in the reooitt s)-stcm. in which, htmtrw, the Uttraoed ia the of^xxnte directioo, or from the toward the trunks j this is seeo in the fonnatioD tlu iafenor cava by the jtuurtioD o( th« two coonw* Uiac vetn». The saute amngeiaeot kIm cxbts, but in aik iofcriur degnw, to th« absorhiog systen. t >.< .,.<TbQ aog^ which the vtHMh form in dividit^ are rarioiu «ize», although they uv genendly rooK or 1 acute, approaching, according to lialler, the measi ment of 45*. The ve&^eU of Uk extresnities diride in branches at a small angle, and the spcnuatic artiTiKST and veins are connected witii the aorta aod tuftrtvr cam respectively, at still more acute aogles. . In the ckcst, in the abdomen, and occasionally in the limbft,] the large vessels form with their trunks, an^W whictki approach 90° ; this is the disposition of the gn.-at arte~- ries whkh arise from the arch of the, aorta ; also uf the intercostal, the coeliac, the articidur, the tanud artertes^t &c. A similar arrangement is obser^'cd in the termina- tions of the renal, lumbar, and internal ju^ar reins ; and likewise in the junction of tbe thoracic duct with the subclavian vein. It occasionally happens that th< angles of division are obtuw, iis in the instances of the« upper intercostal and coronar)- arteries. In some rgore ' rare examples, tbe ai^Ie is so open, that the vessels are recurrent, as in the spinal arteries, and in the recuircnt' vusAels of the different articulations. It has, however,' ' 'been well observed, that those branches which uppear ' to form obtuse angles with the tnmk, come off in rwltty at acute angles, and that it is only from their' immediately forming an inflexion and altering their'' ANASTOMOSIS «F VtSBKLS. 29 course, that they have the ftppeftrance of aming at- it l(irg angle."" vj "v »di ai •'There are but few gentml principles thtit 'c8Ji''bi( itpduced from the preceding observntions concerning [h* rfinsions of Ihp viiscular system. It is endcnt; how'ercr, thftl as this system Ls disposed in the form of a cone, of which the apex corresponds to the heturli tlie Wood; as it passes from that organ towards the distant ramifications of the arterlRl system, must cirJ culote in a space which gradually enlarges ; and on the contrary, that the contents of the veins and absorhents inwtbe propelled through channels which successively deenWc in size as they approach the heart. It vn&gt;i also remarked by Mr. Hunter, that in the ■k-icinity of the 'entricfes the arteries arise at lflrj»e angles, by whidi' mecbimism the force of the circulation is diminished;' while at a distance fiv(m the heart, the branches fonn very small angles xsith their trunks, so that there M^' but little opposition to the free current of the blood. '" A ANASTOMOSIS OF VKSilBLS. „] jiThe various parts of the vascular sj-stem freely com-i" municate in all parts of the body, by means of what' are called amutcmiosing branches. This arrangement i»' more developed in the lymphatics and veins than in the arteries ; the communications are also more frequent iW the small than in the large vessels, although they ara>> uflten observed between trunks of considerable magni-' ' tiidey;<i '"' li. The most ordinary species of anastomosis ig>» that which results from the union of two vessels in ibe-i form of an arch ; this disposition (exists in the vessels of" the mesentery, mesocolon, and kidneys ; it is also met 250 ANAtffOMOSlS OF with MToAnd the joints'.'md goo^rally Id all the BmaBer vessels of thL- body. '''^. The second kind of cotnmunicntioo is established by means of liirge iind UKiially short branches which extend Iielwean two neij^hhourinjf trunks. Such i»ri> the anastomoses of the two anterior cerebral arteries with each other, and of the internal carotid with the pO)<tcnor cerebral, where they form the circle of Willis ; of the two umbilical arteries at their entrance into the placenta ; of the umbilical vein with Ihe interior cava by means of th« canalis ononis ; and, lastly, of the superficial veins atid lymphatics of the extppmities. - 3. The last species of anastomosis, is common in the venous and lymphatic systems, but \ery rare in the arterial ; it U produced by two vesxela uniting at aa acute angle in order to form a third. There are many examples of this disposition in the veins and l^mpbitio of the extremities and trunk ; and also in the uoiotD of the two vertebral arteries where they form the trunk of the basilar, and of the two anterior spinal arteries. nU The connexion by anastomosing branches, is ^neraHJrj established between neighbouring vessels; but there are^ instances of communications being formed between vonr distant tnmk.i. Thus the subclavian and iliac are united by means of the internal mammary epigastric arteries ; and the inferior and superior i cavfc communicate by the ^ena azygos. Many circum^itimces influence (he freedom of anas] tomosis in the different parts of the vascular system. In the first place the communications become more firo- quent in proportion to the minuteness of the and their distance from the heart. This fitct k dered very evident hy cxanuning any transparent paitri ■i.B vBflaam. tolivii^ animal with the microscope, whea it is seen that the small vessels form a most intricate pluxus, in which the lluicU circulate with amazing facility. The situation and Uit^ degree of exposure to which the ves- sels are suhjected, affect, in a striking maimer, the number and size of their inosrulations. Thus, the blood^ve^^sels and lacteaU of the mesentery, which are coutinually influenced by the action of the abdominal muscles, and by the peristaltic motioD of the intestines, are pre-eminently distingimlted by the multitude and volume of their anuKtomosiiig branches. A^^a, in the extremities, Uie articuhur arteries freely communicate, because they are necessarily compressed in the move- ments of the joints; and, for a similar reason, the superficial veins and lymphatics, which are ejtposed on the surtiaioe of the body, unite with each other more frequently than the deeper -sealed vessels. There is still another circumstance that has u decided elfect on the freedom of luiastomoHis : 1 allude to the importance of the organ to ■ which the vessels are distributed. The brain affords a remarkable illustration of tiiis statement: itj is well known that, at the baae of this organ, the arteries ore joined to each other by the large brunches which constitute the circle of Willis. Nature appears to have employed two methods for securing the circulation of the different parts of the body; the first, and the most essential, is the anasto- mosis of the vessels ; the second, which ought, perhaps, to be regarded as subservient to the former, is the trans- missioQ of the fluids which belong to any particular region or organ, through two or more ehunui-ls, in- stead of through one trunk. The latter provision is ex- emplified in the fore arm,wluch possesses four principal 1S9 lMf»nMSl€9 OF Hml dffon^ fear tnfetOr M^eptadeal cHili. Ue <>f bein^ Encreaaed to a sasfnaap ^■— ^i vftaKHT there H mT mtemptkm to tke ordaMT flow af the A^ intemjr flai«k. 1 sfaafi amir ^li^ fW JiDjah^ proofit tn fspport of thu poskioB. The aofta h^ fi^' qiwocH been tied ia »««mK of coasiilerabie liii mlA' perfect SKceK; it has also been foamA taiaely olfie- rated in (fiftrent parts of its mane, in iW hvnna ndK jeet ; in one case the dontre occuwed aa Ufh ■■ the tcnntnation of its cunalurv. Many cases aie iriMted in: whidi the inferior eava, tbe internal jb|.ii1ii . and tke iBae mm, bare been oUitiTalHl ; and Dr. Ifaa^j lii reeorded a cane, in wbicfa tbe sapmor aen and Ike Mk indidavian vein were afanost dosed hr the pRacMeotf an aneonsmal tomoor. Lastly, the trunk of tlidbnb ractc duct has been tied by Flandrin, Dnpuytna, mA othcm, and Rereral of the aninnls recofcrcd. ' It oqghtt to be stated, however, that the last named ihiitiinjawliiJ' pbyftiologist has discovered, that io the aniinyswluoli' * It WM apOQ thn principle tint Ibe modtm opcnItH tm i ytHcmtd ID (he year I7S5 b; Mf. Hunts, Cor tbe cor a( la t Ibe hna. SufaMqaeotty to Aria grand impto^-oBait, tb csiemri bMD Memd bf Mr. Aberoetfa;; the nbcbTiM artery bdow A danEl«1 by Mr. Kcate; (be coiDinoo cuotid, b; Sir A. CoofV; tbei above the eUvicle, by Hr. RamtdeD j (he Ri(enial 0^ utar. by Dr. 1 the Merh ionontnala. by Dr. Mott, o( New Yoit ; aad hHMy, miMi MXtt i(Klf, by Sii A. Cooper. Tbw iHi of dMiagoiibBd auMi ii«B»: aiooDg the many gratifying proob wbicb iiugb( be nwotawed, tf the gnai'.' beocfltt that haTC been conferred on faaokind by the talealt and hdmn «(• EngliA wigtom. ' •■■\ The reader ii wlbrrtd for a ery cacellent accooat of (be nmtaimmt^^ coainMnieo(ioi)t of the arterira Iwlooging' to the iippv tod loi«ares(iBaailie«>h Jo the TmliM on AneurUn, by Scarpa, (miHlated by WUorl, ^ i^.t^rmfii> ANA&TOMOaiNti CUCULATIDN. 29.9 survived, it vroa poxsiblf. to injvct ijuick^^ilwr from the ^doinintU portiun uf the duct into tlie HuWIavian vein^ the mcrcur)' pimsing through some large lympUatio veoseU, which proceeded ftom helow the ltg&tHre,,ftn(t opened in the vein of the neck. r,, ,i.) -lit it aiinmt needless to add, after what has beei^i stated, that the great ug« of aoaatoinosifi is to facilit^ito, the circuhUioo uf the iluids, by preventing any interrupt; tit}n to their current in the vnriouii ot^nns of the body^ , , iJhe vessels, end particulnrly the trunks, generally, pass in a straight direction, so that their course mon, of: less corresponds with the long' axis of the body ;i there arc. however, mimy deviations from Uiis di«po-i aitioni' The small vesscU do not observe any constant arrniigcmcnt, idthougb in raost places they present aili arborescent ur reticulated appearance. The arteries be-i longing to organi> which are suliject to considemUle- changes in their volume, figure, or situation, are ctitttJni, guished by the flexures they describe in their course ;> there are examples, in tlie vciiscls of the uterus during, the colargcmcut of that viscus in pregnancy, in those ofi the stomach, the intciitinBl canal, the lips, tongue, &c.| ■ Tbe most KiTuukaMe lattmce 1 un wquaintid will), of th« powen of Ilw MaMoraMing circulation. CH:i:umd in « dof^ on wliicli my Inlc hmUier, in <feo pMMBoe of loveml of hit fneiidi. ptrioraii^ llii? folluwiag cxiH-iimeob. , fto finttied llic ikbdomiDil noila. nnil when thtuiimal had rccovciixl (lom that opctation, h«»ecut«d, U iaWnilt, ili« carotida aiul l\vi gmt iruuU of ttw witeiiDr extfcrailic^ so thil Ihe whole raucM pf ihe citculMiun mud hava r. bMO literocl. Tlw dog. which wu of leiy Iti^e tiw, iurviv«d ftll ih«)e ope- ratMiit fend appeared lo eDJojr it* ordinary hwltli. It uuluckilji happened, that lhi> animal wai al Birmlaghnn), when no sUcm of hydrophobia pr»>, vailed, and, owing to iiegligmct^, il acaped mto thu i<ltMt>, and wai, in all probability, doilroy^ii by some of Ihe people, who hud orden frotn U>c nugit- , taam to kill all doga foiuid abroad. Alliiough rasny attempt* wer« inad« lo ducovcT ih« liody, they vric uoiuocMafui ', to Ihul litem as no opportunity-. of aatatainiag bj irint fuv channotethccuculalioo waa carried od. baooM. hf wlBcfc iliiiyiii«Ttte cwnM of Ite Uooi it iBBeerially tbAfwtd- In the rttnmtw*. the tatm- ni ela6citr of the wtb toabs np Ifar the de6ci«BCf Of tniwf i!BJ (Mors, wfucn w met wiIb itt the ▼•scvdv Wfttem tit the head and libdofBeB. ' IV raweb are aeaHr STimDetneil,f ihliniigfc tlMvv an many ecevptiona to this obacmlioa The want of ijiuiitrtiy is particnUrfy rvidnt tn th« gnat tnmlu ; as the aorta, arteria innoininata, ad6ae Tctue cavie, thonctc dart, tec. On tlu contrmrr, bi At bead, neck, and extremities, the vessels on the two sidea of the hody nearly rorrt-ipond. Thtr coune of the different msek is mAject to pvat vamtion as to ita extmt, but ^meraUy the braorhes pro- ceed firom their tninkii, in the neigbbourfaood of the organs to whirh they are distributed. In a few in- •ttaoea a contnnr tlinposition is observed ; thus the spermatic veasels take a long course before they reaeh their deHtination ; but even in these cases the cootra- dinion is rather apparent than real, and is readily ex- plained when it is recollected, thnt the tesd-s and o-aria are placed io the fcetus near the aorta and the inferior cava, with which the spcnnatic arteries and veins are respectively connected. The number and the size of the venscLi, nnd, con«^i qucntly, the quantity of fluid which they carry, are cd^H * ll ipfNttn, Uiil Ihr IoiIuoomcb ofatarnl ic certMD vchbIi, depend^ in •OTH caw, on mcmued local Miwn; toA In ollMn, on the ob«ructjon whidi M olSnrd Io Ih (it* cirrulabos of Ibe couUianl fluid*. Tba laOo- OMB cf Um Tanner cnuw it etbitikUd in ih* rlwngn which lh« uMaa i wdngo during gaNrtion ; and thM of the lalter, id Ihe pcoduclnn of i vttai* la dw Icp. t Smp.19. .. NUMBER AND SIZE. ^ 235 I treinely uoeqmd in the different structures of the body. It rarely buppeos that an organ does not receive suvcrul vesiiels, which frequently arc durivt-d from distinct trunks, and which usually <iivide and BniuitomoKu with each other previous to terminating. Tiie Ixxlieii tliat are si- tuated on the median Une, receive two vetisels of the SUM Dune, the one right, and the other left ; this i» Bcoo in the brain and spinal cord, in the nose, tongue, larjnx, bladder, penis. &c. Some of these organs have more than two veKseht, thus tlic brain and tliyroid gland posiieAS four each, and thv: spinal curd receivcK a great number of branches from the arterieii of the neck, chciit, and abdomen. The bones, mu.scles, ner'es, glands, &c. are also euppUed by several arteries which penetrate by different points of their surface. On the contrary, the spleen, the kidney, and the eye, only receive one artery and one vein. fi-i The trterieit, veins, and lymphatics, uAer they have entered the suhstiinee of the organ:), divide and subdi- vide, till at length they become so extremely minute tliat they escape the naked eye. If the microscope is em- ployed, it will be seen that the small branches still coa- tUQue to divide, and that ultimately they form by their communications a very beautiful and intricate plexus. The termination of the vessels offers so many important points for investigation, that I shall defer the wjnsidera- tjon of the subject until the properties of the arterial and venous systems have been described. r iBft NUMBBR or COATS. Skction n. '• ■t "• UftQANIZATION or THE VA8CULAII 8YBTBM. < TuK blood-x-esHels and l^inphnlid are compus(!<l ofi certain layers or tunics, the number and cburactcp.^ which vary considerably in the three ordem of vessdi- In the present day it is admitted that the arteries and veins posM^s three coats, hut with nspoct to the ab- sorbents, they have only two membranes. The internal coat is the most important, because it extends throughout the va.'tcuhir system, nnd nlthouf^ in tlio different divisions of this system modihcations may be observed in its structure, yet it appears to pos- sess in alt parts essentially the Bamu properties. It is very thin, whitish, and olmost traosparfnl ; when ex- amined with the naked eye there is no appearance of 6bres, nor have I been able to delect any with the microscope. Dr. Hotlgkin and Mr. Lister slate, bow- ever, that the internal membrane of the arteries consists of extremely delicate, smooth, and uniform fibres, which are tortuous and malted together in an intricate plexwt. In proportion to its thickness this coat is very dense and resisting, so that it is capable of supporting by itself a considerable column of (quicksilver ; it is also extensible and elastic. The inner surface of the lining membrane is perfectly smooth, and is moistened by a thin and rather unctuous fluid, which has a g^'ent rcscniblaiice to the secretion of the serous membranes. It is an interesting question to determiue what is the source of this liquid. Is it INTBRNAL COAT,lV( formed like the fluid of the peritoneum and similar structures, by a secernijig procesa during lite ; or is it produced after death, as Bichat is inclined to believe, by a