common integuments, that is, by the skin, cellular tissue, and cervical fascia, and is, therefore, easily accessible to the knife in its

Fig. 17. Windpipe.-1. Larynx. 2. Trachea. 3. Right bronchial tube. 4. Left bronchial tube. a. Thyroid cartilage. b. Crico-thyroid membrane. c. Cricoid cartilage.

entire extent. Neither the platysma, myoid, the sterno-hyoid, sterno-thyroid, nor the crico-thyroid are at all interested in any of the forms of laryngotomy; for, as these muscles ascend along the neck, they are separated from each other by a triangular interval, broader above than below, and occupied by the crico-thyroid membrane. A small artery, a branch of the superior thyroid, and hardly as large as a darning-needle, generally runs across the anterior surface of the crico-thyroid membrane, and may, when divided, require the ligature. The posterior surface of the larynx, along the entire middle line, is covered merely by mucous membrane. Hence, if, after the common integuments have been removed from the larynx,

an incision be made through the tube from one extremity to the other, the only parts divided will be the thyroid cartilage, the crico-thyroid membrane, and the cricoid cartilage, with the mucous investment behind.

The interior of the larynx presents several objects of interest and importance in reference to the introduction and egress of foreign bodies; objects which, it need hardly be added, should be well understood by the surgeon, as much of the success of his practice will necessarily depend upon his knowledge of this portion of the windpipe. These objects are, the mouth of the larynx, the glottis and its rima, and the ventricles of Morgagni.

The mouth of the larynx is that portion of the tube which communicates with the pharynx; it is of a triangular form, being wide in front, and narrow behind, and corresponds with the epiglottis, which, when depressed, generally completely covers it. As it is the most capacious part of the larynx, it readily admits foreign bodies, which, from their size, cannot always easily pass through the rest of the organ, and which, becoming arrested there, often produce instant suffocation by their mechanical obstruction to respiration. This portion of the windpipe is sometimes denominated the superior orifice, inlet, or entrance of the larynx.

The glottis is the space between the mouth of the larynx and the vocal cords, which thus form its inferior boundary. It has the form of a long narrow fissure, running from before backwards, and gra dually diminishing in size as it extends from above downwards, es pecially in its transverse diameter. In looking through the inferior part of this space, we see the rima of the glottis, an elongated triangular chink, the base of which is behind, and the sides of which are formed by the inferior vocal cords. This slit-like aperture is the narrowest portion of the canal, and is, therefore, easily choked up by foreign bodies, and even by pieces of adventitious membranes, such as are often formed during the progress of inflammatory affections, particularly croup. In the adult, it is from ten to eleven lines in the antero-posterior diameter, and from three to four in the transverse, which, however, is capable of expanding, during inspiration, to five or six lines, while, during expiration, it has the same breadth as that observable in the dead body. The size of the rima is always less, relatively, in the female than in the male.

In the interior of the larynx, between the two vocal cords on each side, is the ventricle of Morgagni (Fig. 18, 1), a deep, elliptical

pouch, cul-de-sac, or hollow, narrower at its orifice than in its interior, and generally about three-quarters of an inch in length in the

Larynx, laid open posteriorly. 1, 1. Ventricles of Morgagni. 2. Epiglottis. 3. Interior of the tube. 4. Trachea. (From a dissection by the Author.)

full-grown subject. This cavity, which is exceedingly small in infants and children, is of great surgical interest from its liability to entrap extraneous substances, and from the difficulty which the operator sometimes experiences in his attempts at dislodging them. Each ventricle, at its anterior extremity, is supplied with a kind of supplementary cavity, commencing by a broad base, and terminating by a narrow point. In its shape, it is said to resemble a Phrygian cap. Its dimensions are variable. In one instance, it was found to be half an inch in its vertical diameter, but generally, it is much smaller.

The trachea (Fig. 17, 2), situated in the neck and the upper part of the chest, is continuous superiorly with the larynx, and inferiorly

with the bronchial tubes, in which it terminates, generally opposite the third dorsal vertebra. Its mean diameter is from ten to twelve lines in the male, and from nine to ten in the female. Its direction is vertical. The cervical portion, the only one necessary to be noticed here, is usually about three inches and a quarter in length, but of course varies, in this respect, according to the length of the neck. In very young children it is commonly very short, and hardly four lines in diameter. It lies immediately under cover of the sterno-hyoid and sterno-thyroid muscles, the former of which, in their ascent along the neck, are closely united to each other by a white fibrous raphé, indicating the situation of the middle line. Beneath these muscles, which are of a flat, ribbon-like shape, and generally of a deep flesh color, is a layer of the cervical fascia, and in close contact with the tube is the thyroid plexus of veins, enveloped in a small quantity of loose cellular tissue. In very fat subjects, a few granules of adipose matter are also met with here. Occasionally a small artery, the middle thyroid of Neubauer, ascends along the front of the trachea, on its way to the thyroid body, and is liable to be divided in opening the canal. In some instances, though rarely, a few small lymphatic ganglions lie directly in front of the tube; and sometimes, again, but this is also uncommon, a vein of considerable size is seen lying immediately beneath the skin, along the middle line, and consequently directly in the course of the incisions in the operation of tracheotomy. The dis position of the large vessels at the root of the neck, and their relation with the operation of tracheotomy, will be fully pointed out in another section of this work.

The lamella of the deep cervical aponeurosis which envelops the windpipe, and which may hence be denominated the tracheal fascia, is nothing but cellular tissue, in a somewhat condensed state. It is not sufficiently firm, however, to prevent the infiltration of air in tracheotomy, and it has, therefore, been advised, in order to guard against this occurrence, that a portion of this substance should always be excised immediately around the wound at the time of the operation. Such a step, however, I conceive to be altogether unnecessary, and even improper. All that can ever be required is a free division of the membrane, to prevent it from slipping over, and thus occluding the artificial aperture.

The trachea, as it descends along the neck, lies upon the œsopha gus; while on each side it is in relation with the lateral lobe of the

thyroid gland, the great cervical vessels, the pneumogastric nerves, and several lymphatic ganglions. The superior extremity of the tube, opposite the third and fourth rings, is covered by the isthmus of the thyroid gland, which, however, varies a good deal in breadth in different cases, reaching sometimes as high up as the cricoid cartilage, or extending as low down nearly as the middle of the neck. In seventeen persons, whose ages ranged from fourteen to seventy, Mr. Ormerod,' of England, found the distance between the superior border of the isthmus and the inferior border of the cricoid cartilage to be from one-eighth to three-eighths of an inch. In three of the cases the gland was on a level with the cricoid cartilage. It should also be recollected that this body occasionally sends a process upwards over the thyroid cartilage. In nearly one-half of the cases examined by Mr. Ormerod, a branch of the superior thyroid artery was seen coursing along the upper edge of the isthmus. The same writer also observes that it is not unusual to find a large branch of the superior thyroid artery running down vertically from the crico-thyroid membrane, over the cricoid cartilage, to the transverse portion of the gland, and somewhat resembling, in its direction and arrangement, the thyroid artery of Neubauer; while at other times the inferior thyroid veins ascend over these structures, and even over a portion of the thyroid cartilage, to anastomose with the laryngeal and superior thyroid veins.

The space between the inferior edge of the isthmus of the thyroid body and the top of the sternum is the point necessarily selected for performing tracheotomy. The length of this space varies in different individuals, from nine lines to two inches and a quarter in the ordinary position of the neck; but it is always considerably increased, sometimes as much as an inch, or even an inch and a quarter, by forcibly extending the head. As the trachea descends towards the thorax, it gradually recedes from the surface, and in children, and short, fat-necked persons, it not unfrequently lies at a depth of from one and half to two inches. To perform bronchotomy readily and successfully, the operator should render himself perfectly familiar, by frequent touch and inspection, with the consistence and situation of the hyoid bone, the thyroid and cricoid cartilages, the crico-thyroid membrane, and the thyroid body; the course, length, and depth of the cervical portion of the trachea, and its relation to

Clinical Collections and Observations in Surgery, pp. 182-3. London, 1846.