Surgical Anatomy Part 10

H. Transversalis colli artery.

I. Layer of the cervical fascia, which invests the sterno-mastoid and trapezius muscles.

K. Lymphatic bodies lying between two layers of the cervical fascia.

L. Descending superficial branches of the cervical plexus of nerves.

M. External jugular vein seen under the fascia which invests the sterno-mastoid muscle.

N. Platysma muscle cut on the body of sterno-mastoid muscle.

O. Projection of the thyroid cartilage.

P. Layer of the cervical fascia lying beneath the clavicular portion of the sterno-mastoid muscle.

Q. Layer of the cervical fascia continued from the last over the subclavian artery and brachial plexus of nerves.

[Ill.u.s.tration: Right side of the head and neck, showing blood vessels, muscles and other internal organs.]

Plate 8

COMMENTARY ON PLATES 9 & 10.

THE SURGICAL DISSECTION OF THE STERNO-CLAVICULAR OR TRACHEAL REGION, AND THE RELATIVE POSITION OF ITS MAIN BLOODVESSELS, NERVES, &c.

The law of symmetry governs the development of all structures which compose the human body; and all organized beings throughout the animal kingdom are produced in obedience to this law. The general median line of the human body is characterized as the point of fusion of the two sides; and all structures or organs which range this common centre are either symmetrically azygos, or symmetrically duplex. The azygos organ presents as a symmetrical unity, and the duplex organ as a symmetrical duality. The surgical anatomist takes a studious observation of this law of symmetry; and knowing it to be one of general and almost unexceptional occurrence, he practises according to its manifestation.

The vascular as well as the osseous skeleton displays the law of symmetry; but while the osseous system offers no exception to this law, the vascular system offers one which, in a surgical point of view, is of considerable importance--namely, that behind the right sterno-clavicular articulation, C, Plate 9, is found the artery, A, named innominate, this being the common trunk of the right common carotid and subclavian vessels; while on the left side, behind the left sterno-clavicular junction, Q, Plate 10, the two vessels (subclavian, B, and carotid, A,) spring separately from the aortic arch. This fact of asymmetrical arrangement in the arterial trunks at the fore part of the root of the neck is not, however, of invariable occurrence; on the contrary, numerous instances are observed where the arteries in question, on the right side as well as the left, arise separately from the aorta; and thus Nature reverts to the original condition of perfect symmetry as governing the development of even the vascular skeleton. And not unfrequently, as if to invite us to the inquiry whether a separate origin of the four vessels (subclavian and carotid) from the aorta, or a double innominate condition of the vessels, were the original form with Nature, we find her also presenting this latter arrangement of them. An innominate or common aortic origin may happen for the carotid and subclavian arteries of the left side, as well as the right. Hence, therefore, while experience may arm the judgment with a general rule, such generality should not render us unmindful of the possible exception.

When, as in Plate 9, A, the innominate artery rises to a level with C, the right sterno-clavicular junction, and when at this place it bifurcates, having on its left side, D, the trachea, and on its right side, B, the root of the internal jugular vein, together with a, the vagus nerve, the arterial vessel is said to be of normal character, and holding a normal position relative to adjacent organs. When, as in Plate 10, A, the common carotid, and B, the subclavian artery, rise separately from the aortic arch to a level with Q, the left sterno-clavicular articulation, the vessels having M, the trachea, to their inner side, and C D, the junction of the internal jugular and subclavian veins, to their outer side, with b, the left vagus nerve, between them, then the arterial vessels are accounted as being of normal character, and as holding a normal relative position. Every exception to this condition of A, Plate 9, or to that of A B, Plate 10, is said to be abnormal or peculiar, and merely because the disposition of the vessels, as seen in Plates 9 and 10, is taken to be general or of more frequent occurrence.

Now, though it is not my present purpose to burden this subject of regional anatomy with any lengthy inquiry into the comparative meaning of the facts, why a common innominate trunk should occur on the right of the median line, while separate arterial trunks for the carotid and subclavian arteries should spring from the aorta on the left of this mid-line, thus making a remarkable exception to the rule of symmetry which characterizes all the arterial vessels elsewhere, still I cannot but regard this exceptional fact of asymmetry as in itself expressing a question by no means foreign to the interests of the practical.

In the abstract or general survey of all those peculiarities of length to which the innominate artery, A, Plate 9, is subject, I here lay it down as a proposition, that they occur as graduated phases of the bicleavage of this innominate trunk from the level of A, to the aortic arch, in which latter phasis the aorta gives a separate origin to the carotid and subclavian vessels of the right side as well as the left. On the other hand, I observe that the peculiarities to the normal separate condition of A and B, the carotid and subclavian arteries of Plate 10, display, in the relationary aggregate, a phasial gradation of A and B joining into a common trunk union, in which state we then find the aorta giving origin to a right and left innominate artery. Between these two forms of development--viz., that where the four vessels spring separately from the aortic arch, and that where two innominate or brachio-cephalic arteries arise from the same--may be read all the sum of variation to which these vessels are liable. It is true that there are some states of these vessels which cannot be said to be naturally embraced in the above generalization; but though I doubt not that these might be encompa.s.sed in a higher generalization; still, for all practical ends, the lesser general rule is all-sufficient.

In many instances, the innominate artery, A, Plate 9, is of such extraordinary length, that it rises considerably (for an inch, or even more) above the level of C, the sternal end of the clavicle. In other cases, the innominate artery bifurcates soon after it leaves the first part of the aortic arch; and between these extremes as to length, the vessel varies infinitesimally.

The innominate artery lies closer behind the right sterno-clavicular junction than the left carotid or subclavian arteries lie in relation to the left sterno-clavicular articulation; and this difference of depth between the vessel of the right side and those of the left is mainly owing to the form and direction of the aortic arch from which they take origin. The aortic arch ranges, not alone transversely, but also from before backward, and to the left side of the dorsal spine; and consequently, as the innominate artery, A, Plate 9, springs from the first or fore part of the aorta, while the left carotid and subclavian arteries arise from the second and deeper part of its arch, the vessels of both sides rising into the neck perpendicularly from the root in the thorax, will still, in the cervical region, manifest a considerable difference as to antero-posterior depth. The depth of the left subclavian artery, B, Plate 10, from cervical surface, is even greater than that of the left common carotid, A, Plate 10, and this latter, at its root in the aortic arch, is deeper than the innominate artery. Both common carotids, A A, Plates 9 and 10, hold nearly the same antero-posterior depth on either side of the trachea, M, Plate 10, and D, Plate 9. Although the relative depth of the arterial vessels on both sides of the trachea is different, still they are covered by an equal number of identical structures, taking the same order of superposition.

On either side of the episternal cervical pit, which, even in the undissected body of male or female, infant or adult, is always a well-marked surgical feature, may be readily recognised the converging sternal attachments of the sterno-mastoid muscles, L G, Plate 10; and midway between these symmetrical muscular prominences in the neck, but holding a deeper level than them, is situated that part of the trachea which is generally the subject of the operation of tracheotomy. The relative anatomy of the trachea, M, Plate 10, D, Plate 9, at this situation requires therefore to be carefully considered. The trachea is said to incline rather to the right side of the median line; but perhaps this observation would be more true to nature if it were accompanied by the remark, that this seeming inclination to the right side is owing to the fact, that the innominate artery, A, Plate 9, lies obliquely over its fore part, near the sternum. However this may be, it certainly will be the safer step in the operation to regard the median position of the trachea as fixed, than to encroach upon the locality of the carotid vessels; and to make the incision longitudinally and exactly through the median line, while the neck is extended backwards, and the chin made to correspond with the line of incision. And when the operator takes into consideration the situation of the vessel A, Plate 9, and A, Plate 10, at this region of the neck, he will at once own to the necessity of opening the trachea, D, Plate 9, M, Plate 10, at a situation nearer the larynx than the point marked in the figures. The course taken by the common carotid arteries is, in respect to the trachea, divergent from below upwards; and as these vessels will consequently be found to stand wider apart at the level of K, I, Plate 10, than they do at the level of M, Plate 10, so the farther upwards from the sternum we choose the point at which to open the trachea, the less likely are we to endanger the great arterial vessels.

In addition to the fact, that the carotid arteries at an inch above the sternum lie nearer the median line than they do higher up in the neck, it should always be remembered, that the trachea itself is situated much deeper at the point M, Plate 10, D, Plate 9, than it is opposite the points F and K of the same figures. The laryngo-tracheal line is, in the lateral view of the neck, downwards and backwards, and therefore it will be found always at a considerable depth from cervical surface, as it pa.s.ses behind the first bone of the sternum, midway between both sterno-mastoid muscles.

In the operation of tracheotomy, the cutting instrument divides the following named structures as they lie beneath the common integument: If the incision be made directly upon the median line, the muscles F, sterno-hyoid, and E, sterno-thyroid, Plate 9, are not necessarily divided, as these structures and their fellows hold a somewhat lateral position opposite to each other. Beneath these muscles and above them, thus encasing them, the cervical fascia, f f, Plate 10, is required to be divided, in order to expose the trachea. Beneath f f the cervical fascia, will next be felt the rounded bilobed ma.s.s of the thyroid body, lying on the forepart of the trachea; above the thyroid body, the cricoid and some tracheal cartilaginous rings will be felt; and since the thyroid body varies much as to bulk in several individuals of the same and different s.e.xes, as also from a consideration that its substance is traversed by large arterial and venous vessels, it will be therefore preferable to open the trachea above it, than through it or below it.

On the forepart of the tracheal median line, either superficial to, or deeper than, the cervical fascia, the tracheotomist occasionally meets with a chain of lymphatic glands or a plexus of veins, which latter, when divided, will trammel the operation by the copious haemorrhage which all veins at this region of the neck are p.r.o.ne to supply, owing to their direct communication with the main venous trunks of the heart; and not unfrequently the inferior thyroid artery overlies the trachea at the point D, Plate 9, when this thyroid vessel arises directly from the arch of the aorta, between the roots of the innominate and left common carotid, or when it springs from the innominate itself. The inferior thyroid vein, sometimes single and sometimes double, overlies the trachea at the point D, Plate 9, when this vein opens into the left innominate venous trunk, as this latter crosses over the root of the main arteries springing from the aorta.

Laryngotomy is, anatomically considered, a far less dangerous operation than tracheotomy, for the above-named reasons; and the former should always be preferred when particular circ.u.mstances do not render the latter operation absolutely necessary. In addition to the fact, that the carotid arteries lie farther apart from each other and from the median place--viz., the crico-thyroid interval, which is the seat of laryngotomy--than they do lower down on either side of the trachea, it should also be noticed that the tracheal tube being more moveable than the larynx, is hence more liable to swerve from the cutting instrument, and implicate the vessels. Tracheotomy on the infant is a far more anxious proceeding than the same operation performed on the adult; because the trachea in the infant's body lies more closely within the embrace of the carotid arteries, is less in diameter, shorter, and more mobile than in the adult body.

The episternal or interclavicular region is a locality traversed by so many vitally important structures gathered together in a very limited s.p.a.ce, that all operations which concern this region require more steady caution and anatomical knowledge than most surgeons are bold enough to test their possession of. The reader will (on comparing Plates 9 and 10) be enabled to take account of those structures which it is necessary to divide in the operation required for ligaturing the innominate artery, A, Plate 9, or either of those main arterial vessels (the right common carotid and subclavian) which spring from it; and he will also observe that, although the same number and kind of structures overlie the carotid and subclavian vessels, A B, of the left side, Plate 10, still, that these vessels themselves, in consequence of their separate condition, will materially influence the like operation in respect to them. An aneurism occurring in the first part of the course of the right subclavian artery, at the locality a, Plate 9, will lie so close to the origin of the right common carotid as to require a ligature to be pa.s.sed around the innominate common trunk, thus cutting off the flow of blood from both vessels; whereas an aneurism implicating either the left common carotid at the point A, or the left subclavian artery at the point B, does not, of course, require that both vessels should be included in the same ligature. There seems to be, therefore, a greater probability of effectually treating an aneurism of the left brachio-cephalic vessels by ligature than attaches to those of the right side; for if s.p.a.ce between collateral branches, and also a lesser caliber of arterial trunk, be advantages, allowing the ligature to hold more firmly, then the vessels of the left side of the root of the neck manifest these advantages more frequently than those of the right, which spring from a common trunk. Whenever, therefore, the "peculiarity" of a separate aortic origin of the right carotid and subclavian arteries occurs, it is to be regarded more as a happy advantage than otherwise.

DESCRIPTION OF PLATES 9 & 10.

PLATE 9.

A. Innominate artery, at its point of bifurcation.

B. Right internal jugular vein, joining the subclavian vein.

C. Sternal end of the right clavicle.

D. Trachea.

E. Right sterno-thyroid muscle, cut.

F. Right sterno-hyoid muscle, cut.

G. Right sterno-mastoid muscle, cut.

a. Right vagus nerve, crossing the subclavian artery.

b. Anterior jugular vein, piercing the cervical fascia to join the subclavian vein.

[Ill.u.s.tration: Neck and upper chest, showing blood vessels, muscles and other internal organs.]

Plate 9

PLATE 10.

A. Common carotid artery of left side.

B. Left subclavian artery, having b, the vagus nerve, between it and A.

C. Lower end of left internal jugular vein, joining--

D. Left subclavian vein, which lies anterior to d, the scalenus anticus muscle.

E. Anterior jugular vein, coursing beneath sterno-mastoid muscle and over the fascia.

F. Deep cervical fascia, enclosing in its layers f f f, the several muscles.

G. Left sterno-mastoid muscle, cut across, and separated from g g, its sternal and clavicular attachments.

H. Left sterno-hyoid muscle, cut.