2. An important subject for mention, in re gard to the surgical anatomy of the neck, is the provision for collateral circulation, when the main trunks are obliterated. Mr. Burns, in discussing the question of tying the arteria innominata, speaks of these natural resources in the spirit of confidence, which has been familiar to English surgery, since the time of its profound lawgiver, John Hunter " We entertained no dread of the circulation being supported in the right arm ; nay, we reduced it to a demonstration. On the dead subject, I tied the arteria innominata with two ligatures, and cut across the vessel in the space between them, without hurting any of the surrounding vessels. Afterwards, even coarse injection impelled into the aorta, passed freely by the anastomosing vessels into the arteries of the right arm, filling them and all the vessels of the head conipletely." The fluid passed (as the blood would, under similar circumstances, pass in the living subject) from the carotid of the left side to that of the right, through the mesial inosculations of the thyroid, lingual, facial, temporal, occipital, and (not least) ce rebral arteries: from the left subclavian, in like manner, chiefly through the thyroid and ver tebral branches ; and thus a regurgitant stream would flow into the main vessels, up to the very site of ligature. Partly through the con tinued trunk of the tied vessel, so reinforced by its fellow, and partly by secondary commu nications (a.s of the occipital with the cerviealis profunda, of the facial with the internal max illary, of the pharyngeal and palatine arteries) the blood is distributed in its legitimate desti nation. If the subclavian alone be obliterated at its commencement, the inferior thyroid and vertebral (communicating with their fellows, but still more largely with the carotid of the same side) helped by the muscular branches of the occipital, will convey the derived current. If the lig-ature have been applied beyond the scaleni, the transverse branches of the thyroid axis, bytheir free inosculations with the articular branches of the axillary, and with its subsca pular branch, abundantly restore the circula tion. Should the carotid have been tied, its mesial communications, already mentioned, es pecially those within the skull, and about the thyroid gland,—assisted at those places and elsewhere by anastomoses with the subclavian, —adequately fulfil their vicarious duty. So abundant are these various communications, that the lig,ature of a ma:n trunk, in the dead subject, in no degree interferes with the dis tension of its branches by fine injection : if we inject water, or any equally fluid material, through one carotid artery, it freely returns by the other. Under these circumstances, it ex cites our surprise that the cure of aneurism by ligature should be so certain ; for the amount of circulation through the affected vessel can at first be little affected, and the arrest and ulti mate cure of the disease niust be referred rather to the withdrawal of a distensive impulse than to any considerable derivation of current. It seems to have been considered, in operating for aneurism, that, so long as no large branch arose from the vessel closely on the cardiac side of the ligature, it mattered not what branches might arise on its distal side,—how large, or how near. In many instances secon dary hwmorrhage, inducing death, has mani festly depended on defective adhesion at the distal side of the ligature, and for an ob vious reason. The condition of that part of the
artery has been neglected : it has been thought unimportant though a large vessel should arise just beyond the ligature ; or, if a great length of artery have been injudiciously denuded, the cardiac portion has had an exclusive preference of security given to it, by the ligature being drawn as high as possible in that direction. If an equal attention were bestowed on both sides of the'proposed seat of ligature,—if like care were taken, in both directions, to avoid the likelihood of disturbance to the adhesive process by side currents,—if, where the artery has been much denuded, (instead of a single thread being applied at the cardiac extreinity of that isolated portion, by which plan the succeeding part of the tube,—though sepa rated from its connexions, and likely to ulce rate or slough,—is yet left open to the stream of recurrent blood,) a second ligature were placed at the distal limit of the endangered part, there would seem no greater reason to anticipate the occurrence of secondary hatmor rhage than when arteries are tied after an am putation.
3. Anomalous arrangement of the cervical vessels is a contingency which the surgeon must bear in mind Illost of these are com prehended in the abnormalities of the arch already described. (See AORTA.) The ex istence of a median inferior thyroid artery, de rived ftom the arch, or from the arteria inno minata ;—the irregular passage of the right subclavian artery from the left side, behind the cesophagus, or between that tube and the tra chea ;—an early division of the carotid, even to nearly the level of the sternum, or so late a one, that the common trunk furnishes many, or most, of the branches normally originating from the external ;—the absence of an arteria innominata, its branches arising kparately from the arch, or in irregular combination with those of the left side ; the occasional origin of the vertebral from the common carotid,* are the deviations which it most behoves the prac titioner to remember.
4. Certain veins in the neck have an anato mical disposition, rendering them liable, when opened in surgical operations, to become chan nels for inspiration of air to the cavities of the heart, the fatal tendency of which is well known. The internal jugular, innominatie, and subclavian veins are, as 111. Berard notices, " at the root of the neck, so firmly united by fascial laminw and cords to the adjacent bones and muscles, that they do not collapse on divi sion, but gape:" and it is obvious that this cir cumstance (but for which they would be flat tened, and rendered impervious, by the atmo spheric pressure on their outward surface) must expose them remarkably (perhaps alone) to a dangerous participation in the inhaustive move ments of breathing. M. Velpeau (who has written a paper of excellent critical research on the suhjectf) recommends the following pre cautions in approaching veins of the nature described (veines canaliges): studiously to avoid wounding them,—to detach no deeply fixed tumour from its adhesions, without having previously commanded the vessels at its base,—and to maintain no unnecessary ten sion on the fasci, by forced positions of the shoulder.