2. The antero-inferior triangle adjoins in wardly the space last described, is bounded outwardly by the decussation of the omo-hyoid muscle (which sepamtes it from the superior compartment of the great anterior triangle) with the imaginary diagonal, which demarks it from the postero-inferior or supra-clavicular space. Its various parts and contents require some separate description. As reg,ards the inte guments, it will be remembered that the pla tysma only partly covers this space, and that the anterior jugular vein, when it exists, is con tained here in the lower part of its course. The sterno-cleido-mastoideus follows the outer side of the triangle, but extend over it by its sternal border, so as to cover a large portion of its area. Beneath this muscle, the stronger deep layer of the cervical fascia is extended and splits internally to enclose the sterno-thyroi dens, which likewise encroaches on the space by its inner side. Under this fascia the common carotid artery (beside which are the jugular vein and the pneumogastric nerve) ascends ver tically, and is slightly overlapped from within by the thyroid body. The anatomy of the space is well developed, in considering the best mode of reaching the carotid artery: a vertical inci sion falling on the sterno.clavicular joint ex poses the superficial fascia and part of the pla tysma ; these being divided, the sheath of the sterno-mastoid is seen, and on its being opened the stemal fibres of the muscle present them selves, obliquely ascending outward : their di vision and displacement exposes the posterior layer of their fascial investment, which is here seen to ensheath the sterno-thyroid muscle: the descending branch of the lingual nerve (de scendens noni) seems almost embedded in the deep layer of the aponeurosis, and reaches the outer edge of this muscle in the upper part of the space:—beneath the stratum of parts so constituted, the carotid lies with the associated organs : the jugular vein is on its outer side, the nervus vagus lies deeply between the two vessels and behind them ; the cellular mem brane, which invests and binds thein 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 ate capable of caus ing 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 in terposed between them and the sympathetic nerve, which descends vertically behind : se parated in like manner from the great vessels, we find the inferior thyroid artery, which as cends in an obliquely serpentine course to the lower angle of the thyroid body, and the recur rent laryngeal nerve, mounting (on a plane deeper than that artery, internal to which it is situated) toward the posterior part of the cri coid cartilage; the nerve is therefore very nearly approached to the hindermost part of the tra cheal cartilages, and, on the left side, ascends between them and the cesaphagus, closely ap plied to the latter.* The thyroid body belongs to this space by its lateral parts, and, when of mokrate develop ment, overlaps the carotid sheatlb 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 up ward ; they are plump outwardly where the fascia gives them a smooth envelope, but hol lowed inwardly vvhere they adapt themselves to the air-tube : the isthmus commonly con nects the lobes by their lower part only, by over bridging 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 infre quently 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 ceconomy, it readily falls into the heterogeneous group which the German anatomists have named " Blood gangl ia" (blut-knoten). Ft om the same circum stance, and from the probably vicarious func tion which it seems to discharge, it is extremely Irable to hypertrophy, the different forms of which, attended by whatever structural change, are confounded under the name of goitre or bronch-ocele. 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 com municate to it, a general thrill of distensive pulsation, arising from its own almost erectile vascularity, may be felt by the surgeon. Su perficial 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 goitres by the knife have been almost super seded by the discovery, that iodine exerts a marked controul over many enlargements of the thyroid body ; and it would evince other boldness than that of knowledge, lightly to undertake the excision of a tumour so impor tantly connected. The jugular vein, the caro tid artery, the pneumogastric nerve, which on each side the diseased body would overlap, —the trachea and cesophagus, which it would almost encircle, might indeed be avoided in an attempt at its removal ; but the enormous ve nous as well as arterial hmmorrhage that must occur, and the extreme likelihood of dividing the recurrent nerves, would involve a not small possibility of accelerating the fatal result, and deter every prudent surgeon from attempting an operation of sueh extraordinary risk, except under circumstances that might justify the most favourable remote prognosis. The ligature of its nutrient arteries has been advocated as a cure for bronchocele ; but, although this mode of procedure presents fewer anatomical difficul ties than that last mentioned, yet, from surgical considerations of its extreme uncertainty and unsafe protraction, it seems little entitled to preference.
On the left side, the (esophagus, inclining from the median line, presents itself in the antero-inferior triangle. It only half emerges from behind the trachea (which still covers its right portion), and closely lies on the vertebrx : it continues the canal of the pharynx, from a line of abrupt distinction opposite the lower edge of the cricoid cartilage, downward. It is at its commencement that this tube most fre quently interests the surgeon, by becoming the seat of stricture, or by arresting and fixing foreign bodies. To this space the operation of cesophagotomy belongs; and the left side is, for obvious reasons of convenience, chosen for its performance. In AIr. Arnott's instructive paper on the subject the following directions occur, which may serve to illustmte the ana tomy.of the region in iegard of the operation in question: " The situation of the external in cision will, in some measure, depend upon that of the body to be reinoved, but as the pharynx, tapering gradually in its descent, ter minates in the cesophagus immediately under the larynx, it is here that a bulky substance is most apt to be detained. In reaching the
cesophagus at this place, taking as a centre a spot corresponding to the level of the lower margin of the cricoid cartilage and the first ring of the trachea, the only parts of conse quence, whose injury is to be dreaded, are the inferior thyroideal artery and recurrent nerve, (the superior thyroideal artery being too high to run any risk ;) but these will not be wound ed, if the same plan is adopted as that in the case related, of separating the deeper-seated parts by the handle of the scalpel and the finger instead of by the knife. Ilere they were not seen during the operation, in fact they were not within the sphere of the wound, for, on examining the parts after death, the artery and nerve were found below and on the inner side of it. Still I am satisfied by trials on the dead body, that the artery is likely to be di vided if the operation is completed by the knife, and hence the expediency of proceed ing deliberately, cutting but little at a time, sponging carefully, so as to see and avoid the artery, if possible, or to tie it immediately when cut. The recurrent nerve runs less risk as it reaches the side of the trachea, to which it is attached in its ascent, lower down. I do not allude to the carotid artery as being ex posed to any peril. I think, with Mr. Allan Burns, that he must be wanton indeed in the use of his knife, who hurts this vessel. In making the incision into the cesophagus, it is to be remembered that the recurrent nerve runs in the angle between this tube and the trachea, and therefore the incision is to be made a little behind this angle." • 3. 'intern-superior triangle.— This pretty nearly corresponds to the depression which in lean subjects is seen at the side of the neck beneath the jaw and in front of the sterno cleido-mastoid muscle. It is bounded behind by the diagonal line to which sve have so often referred ; the posterior belly of the digastric and the superior belly of the omo-hyoid con stitute, respectively, its upper and lower bor ders, and their convergence to the hyoid bone anteriorly forms its apex. The fascia super ficialis, enclosing the platysma myoides, ex tends uninterruptedly over its borders; and the cervical aponeurosis splitting at each, extends singly over the area which they enclose: the tmnsverse processes of the vertebrs, covered by muscular attachment and by the pre-verte bral aponeurosis, form its floor. The common carotid artery enters it below, and, at about the level of the lower border of the third vertebra, divides into the internal carotid, which con tinues to the cranium the direction of the trunk, and the exteinal, which runs and ramifies in more superficial parts; the sympathetic, as in other regions of the neck, lies between the posterior layer of the sheath of the vessels and the pre-vertebral fascia ; the superior laryngeal nerve lies in the same interval, obliquely bend ing from above to the posterior part of the thyro-hyoid membrane behiLd the vessels : it is on the confines of this triangle and the di gastric space that the posterior belly of that muscle, accompanied by the stylo-hyoid mus cle above and the lingual nerve below, arches across the external and internal carotids, and at about thislevel the stylo-glossus and stylo-pha ryngeus with the glosso-pharyngeal nerve in tervene between those large arteries. It is only below this crossing that the vessels fall under our present consideration, and their study may be facilitated by extending an arbitrary line of division from the os hyoides ( t the apex of the space) transversely backward. Such a line would have below it the trunk, bifurcation and continuing branches of the common carotid, and the origin from the external of the supe rior thyroid artery alone; while, above the level referred to, the continued secondaiy tninks would be seen, and many of the branches which spring from the external one, viz. the occipital passing obliquely toward the mastoid process, under cover of the posterior belly of the digastric, and hooked round by the hypo glossal nerve; the muscular, which is not in variably present, inclining outward to the sterno-mastoideus; the lingual and facial (di vided by an imaginary prolongation of the cornu of the os hyoides from the superior thy roid) entering the digastric space, the former transversely by running along the cornu ,of the os hyoides between the hyo-glossus and middle constrictor, the latter more obliquely ascending; and the pharyngeal artery deeply running upward beside the pharynx. To all these branches a more particular descrip tion has been given in a previous article, than would be suitable to the present one ; and to that the reader is referred for the details of their distribution. (See CAROTID.) The jugular vein descends externally to the in ternal, as to the common carotid, the vagus lying, as in the lower region of the neck, be tween the two vessels and rather behind them. The vein receives several branches, in travers ing this triangle, froin the larynx and tongue, and usually the facial vein : all these, since they come from within, must_ cross in front of the artery, and sometimes form an intricate plexus, which much embarrasses an operator. In front of the sheath descends, with a slight inward obliquity., the branch of the lingual nerve, which at the lower part of the space, and while lying over the vein, forms a reversed arch of communication with the cervical plexus, whence branches are distributed to the sub hyoid muscles. The integuments and pla tysma require no particular notice; their veins and nerves have already been described ; among the former must be reckoned the an terior jugular ; the space contains a great num ber of lymphatic glands, a long chain of which ( glandake concatenatie) lies along the outer side of the sheath of the vessels, while some also lie about the thyroid and lingual arteries on the inner side of the sheath. The surgical relations of this space are chiefly confined to the arteries : ligature of the common carotid or of either of its branches may easily be per formed here, since the vessels lie under a much less thickness and variety of parts than below. A vertical incision falling on the point of inter section of the omo-hyoid and sterno-mastoid muscles, and successively dividing the super ficial fascia (in which the platysma and cuta neous nerves are contained) and the cervical aponeurosis (a single layer, as it stretches across the space, but, of course, double where it encloses the sterno-mastoid,) exposes the sheath of the vessels, the veins which trans versely cross its arterial portion, and the de scendens noni which runs on the part of its wall corresponding to the jugular vein : and here, as he might open the sheath lower or higher, the surgeon would expose the common carotid or its branches ; and, in remembering that the internal (so named from its distri bution only) lies at first external to and behind the other, he would be able to isolate and secure either of these at his option. In any attempt to tie the branches of cle external carotid, a clear notion of their repective re lations to the hyoid bone is of indispensable necessity ; and, in ascending toward the di gastricus, it must be remembered that the lingual nerve crosses the carotid sheath but just below the border of that muscle, and that it and the facial vein are consequently exposed to injury. Attempts at suicide by cutting the throat seldom succeed; the incision is usually made closely either above or below the hyoid bone; in the former case entering the digastric regions, and dividing, with the muscles of the tongue, the lingual and perhaps the facial artery; in the latter case, traversing the thyro hyoid membrane, penetrating the pharynx, per haps implicating the epiglottis, dividing the thyroid artery, and very rarely reaching the external carotid. The mode of searching for these vessels must vary according to circum stances, but, in all essential particulars, may readily be deduced from their anatomy.