the nervus vagus lies deeply between the two vessels and behind them; the cellular membrane, which invests and binds them together, appears to form an indistinct septum to isolate the artery; crossing the front of the sheath,—from the median line toward the jugular trunk, opposite which they pierce—are many veins, of which some are occasionally considerable in size: they are branches from the larynx, trachea, thyroid body, and sub-hyoid muscles, and among them, when it exists, must be counted the anterior jugular: they are capable of causing much inconvenience to the operator, and require to be carefully managed: on the left side, the internal jugular vein itself, inclining toward the median line below, slightly overlaps the artery; the posterior layer of the sheath of these vessels is a thin process of the fascia interposed between them and the sympathetic nerve, which descends vertically behind: separated in like manner from the great vessels, we find the inferior thyroid artery, which ascends in an obliquely serpentine course to the lower angle of the thyroid body, and the recurrent laryngeal nerve, mounting (on a plane deeper than that artery, internal to which it is situated) toward the posterior part of the cricoid cartilage; the nerve is therefore very nearly approached to the hindermost part of the tracheal cartilages, and, on the left side, ascends between them and the œsophagus, closely applied to the latter.[1]
The thyroid body belongs to this space by its lateral parts, and, when of moderate development, overlaps the carotid sheath. It consists of symmetrical lobular halves, united by the isthmus already alluded to: its lobes are pear-shaped, on a section, the small end being upward; they are plump outwardly where the fascia gives them a smooth envelope, but hollowed inwardly where they adapt themselves to the air-tube: the isthmus commonly connects the lobes by their lower part only, by overbridging the trachea at about its second and third rings: the apex of each lobe reaches to the ala of the thyroid cartilage, covering the fibres of the constrictor pharyngis, which arise there, and receiving the superior thyroid artery from the external carotid; the circumference of the organ presents, then, upward a crescentic sinus in which the angle of the thyroid cartilage, the crico-thyroid membrane and muscles, the cricoid cartilage, the first one, two or three rings of the trachea are seen: its thick outer margin,—running from the apex to the third, fourth, or fifth ring of the trachea—corresponds in that extent to the carotid artery, which it more or less overhangs, and below to the recurrent nerve of the larynx; by the extremity of this border the inferior artery reaches it from the thyroid axis; the inferior margin gives exit to veins, which have already been mentioned, and not infrequently receives by its middle a fifth artery from the arch of the aorta or from the arteria innominata.
From the remarkable vascularity of this body, so disproportionate to its volume and apparent unimportance in the œconomy, it readily falls into the heterogeneous group which the German anatomists have named “Blood-ganglia” (blut-knoten). From the same circumstance, and from the probably vicarious function which it seems to discharge, it is extremely liable to hypertrophy, the different forms of which, attended by whatever structural change, are confounded under the name of goître or bronchocele. From the account given of its anatomy, the symptoms of its enlargement may be surmised; for it is obvious that a tumour, so related to the windpipe and so checked in its outward growth by tense aponeuroses, must gravely affect respiration. Overlapping the common carotid arteries, the tumour derives from them a strong and often visible impulse; and, over and above the jerk, which they communicate to it, a general thrill of distensive pulsation, arising from its own almost erectile vascularity, may be felt by the surgeon. Superficial observation might fail to distinguish such a tumour from carotid aneurism, but anatomy establishes the diagnosis; for, in each movement of deglutition, the diseased mass accompanies the larynx, and is seen to rise and fall in the neck. Attempts at extirpating
- ↑ The cardiac branches of the sympathetic,—although they require notice in connexion with the anatomy of the large vessels,—have little particular interest in regard of the surgical operations, which are practised on these, and some account of them is therefore better appended in a note than blended with the text. They are seldom or never distinctly seen in operations; and the rule for their management is but a part of the general principle (which ought to be supreme in every surgical exposure of an artery, and the neglect of which has been, I doubt not, at the root of most unsuccessful issues) that the disturbance of surrounding parts, and the denudation of the artery, should both be in the very least degree, which will permit the ligature of the vessel to be accomplished. The cervical cord of the sympathetic lies, as already mentioned, behind the sheath of the cervical vessels, and presents three ganglia, from which, and from the cord, various branches originate. Of these ganglia,—the uppermost has often above an inch in length, is of tapering rounded form, and is situated in the posterior pharyngeal region, on the second and third vertebræ: the second, of smaller size and inconstant occurrence, usually lies upon the inferior thyroid artery: the third, frequently confused with the first dorsal ganglion, is deeply imbedded behind the origin of the vertebral artery. From these sources, assisted and reinforced by the pneumo-gastric and other nerves, the cardiac branches originate in a manner and succession which will be described in a future article. (See Sympathetic Nerve.) In descending, they lie posterior to the sheath, and the superior one internally to it, close to the trachea, and, on the left side, to the œsophagus. When they approach the inlet of the thorax, they comport themselves variously in regard of the subclavian artery; sometimes passing behind it, on each side, and furnishing twigs, which cross its anterior surface; sometimes, on the contrary, crossing its front by their main branches; and sometimes so dividing as to envelop the artery in an abundant nervous plexus. They are very irregular; but, in all cases, largely communicate with the recurrent nerves, behind the subclavian arteries, and furnish numerous continuations, which descending around the three great vascular trunks to the arch of the aorta, hence prolong themselves to the base of the heart.
