Page:Muscles and Regions of the Neck.djvu/16

14 trachea, passes the inferior thyroid venous plexus, on a level with which would be found, in rare cases, the middle thyroid artery (of Neubauer) ascending from the aortic arch: these vessels are covered by a layer of fascia dividing them from the sterno-thyroid muscles. These parts are variously involved in the two remaining modes of bronchotomy; one of which—the tracheal—consists in dividing three or four rings of the tube, below the isthmus of the thyroid gland; the other—the crico-tracheal—in dividing its upper rings and with them the cricoid cartilage of the larynx. The first—tracheotomy—(after a vertical division of the tegumentary parts and a separation of the muscles from the lower part of the larynx to the sternum) exposes the tube in that portion of its extent in which it is deepest and most nearly related to vessels. The operator is required to bear in mind the possible presence of a middle-inferior thyroid artery, lest he wound it inadvertently; he must avoid, or, before opening the air-tube, must secure the inferior thyroid veins; in recollecting the great lateral mobility of the trachea and its close parallelism to the carotid arteries in the lower part of the neck, he must guard against any oblique glancing of his knife, by which these great vessels might be injured; in proceeding to divide the cartilaginous rings, he must commence below and on a completely exposed part of the tube, and with the blunt border of his knife toward the middle line of the sternum, and with its point directed slightly upward, lest (as might happen in neglect of these precautions) the great vena innominata, transversely crossing the tube just below the level of the sternum, or the large arterial trunks, which are there diverging from the median line, should sustain injury: nor must he rudely transfix the tube and encounter the risk of puncturing parts, normally or abnormally behind it. The second operation, crico-tracheotomy, first proposed by Boyer, pretends to preference over that just mentioned, on the ground of obtaining an equally free opening with less invasion of important parts. Indeed, although M. Boyer, in proposing it, seems to have considered the section of the thyroid isthmus inevitable, and accordingly included its division in his estimate of risks,—perhaps even that objection might be withdrawn from the operation, if performed in exact agreement with his description; since the finger may depress the thyroid body to an extent which admits a safe division of the first two rings of the trachea. But it seems to have escaped his notice, while theorising on the operation, that a section of the cricoid cartilage must be useless, unless abused; that a rigid ring, divided at one point of its circumference, remains unloosened; that a single section of the cricoid cartilage could not be made available as a means for increased access to the air-tube, over and above that afforded by division of the trachea, except by employing on it a disruptive force, that should effect a counter-fracture at some other part of its circumference. Such violence on such an organ M. Boyer was far too judicious a surgeon to have sanctioned; and from the single instance, appended (p. 142 bis) to his speculations on the subject, it appears probable that the upward extension of his opening in the air-tube was useless; that an incision through the upper rings of the trachea sufficed for the escape of the foreign body; and that, in all essential particulars, the crico-tracheal operation is but tracheotomy at a higher than ordinary level, complicated with an unadvantageous and therefore objectionable intrusion on the larynx.

2. The antero-inferior triangle adjoins inwardly the space last described, is bounded outwardly by the decussation of the omo-hyoid muscle (which separates 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 regards the integuments, it will be remembered that the platysma only partly covers this space, and that the anterior jugular vein, when it exists, is contained 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-thyroideus, 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 vertically, 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 incision falling on the sterno-clavicular joint exposes the superficial fascia and part of the platysma; these being divided, the sheath of the sterno-mastoid is seen, and on its being opened the sternal fibres of the muscle present themselves, obliquely ascending outward: their division 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 (descendens 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,