In performing, then, either the superior or inferior operation of tracheotomy, after cutting through the skin and superficial cervical fascia--which is really loose areolar tissue containing fat--the superficial layer of the deep cervical fascia is reached, and immediately below it more or less adipose tissue and the two anterior jugular veins lying in an inferior tracheotomy to either side of the wound, which is always made in the median line. As a matter of fact, these various layers are rarely demonstrable, and the surgeon proceeds irrespective of them until he reaches this point in his operation--viz. the muscles which overlie the trachea. These may overlap in the median line, and have to be retracted after having been separated; or, again, a thin line of connective tissue marks a slight interval between their inner edges, and is readily seen and dissected through if the operator has kept his incision vertical and strictly in the median line of the neck--a matter so important to the success of his operation that I do not hesitate to again allude to it. The muscles separated and gently retracted, together with the overlying tissues, toward the sides of the wound, the upper edge of the isthmus of the thyroid gland overlying the second and third, perhaps fourth, rings of the trachea, is always seen in a superior tracheotomy--its lower edge very frequently in the inferior operation. The isthmus is adherent to the trachea and to the larynx through the deep layer of the deep cervical fascia, but is capable of being slightly displaced or pushed upward or downward as the case may be, and thus kept from obscuring the operative field. This being done, the deep layer of the deep cervical fascia is seen covering and strongly adherent to the tracheal wall together with the thyroid veins. A few touches of the knife, carefully avoiding the blood-vessels, serve to clear it away, and the tracheal rings are clearly exposed. In carrying out this dissection, which has been described as occurring in an ordinary and uncomplicated adult case, several matters must be borne in mind; and especially is this true if the operation concerns infants. In them, for instance, the thymus gland rises half an inch above the level of the sternum, and is frequently to be found as late as the sixth or seventh year. In both adults and children the innominate artery occasionally comes into view in an inferior tracheotomy, obliquely crossing the lower portion of the right half of the trachea. It is relatively higher in the child than in the adult. The left innominate vein is also often observed when the trachea is opened low down.