2. The sterno-thyro-hyoidei muscles, lying under the first pair,
also have to be divided, being similarly united.
3. The trachea, which is fully exposed when the above muscles
are disunited.
THE MANNER IN WHICH THE CARTILAGES
OF THE TRACHEA ARE TO BE EXCISED.
At the commencement, when the operator has leisure, he generally does not cut too deep. The first incision fairly divides the skin and panniculus carnosus quite in the middle of the neck, and is rather longer than a by-stander would deem to be absolutely necessary. The elasticity of the skin will somewhat shorten the opening, while the torture of repeated enlargements will be avoided, and the more important structures beneath the skin will be fairly brought into view.
In the center of your division will appear two long muscles, joined together by a fine cellular union; that union you are to separate; it consists only of cellular tissue, and will necessitate more care than exertion. Underneath the divided muscles will be found two others, smaller and paler, but also joined together by means of fine cellular tissue. These are also to be sundered, and then the trachea lies exposed. There is neither nerve, nor artery, nor vein to avoid, nor to take up in the performance of tracheotomy. All consists in making your primary incision large enough, and, subsequently, in not attempting more than the division of two pairs of muscles.
The commencement of the incision should be made at the spot already indicated. After the skin is cut through and the muscles are divided, two assistants should be obtained to hold them back, while a circular piece is excised from the cartilages of the exposed trachea.
The trachea is formed of numerous cartilaginous rings each half an inch wide, but so united by elastic tissue that the whole forms one continuous tube reaching from the head to the chest of a horse. If possible, only two of these rings are to be interfered with; that is, a half circle, should be cut out of each, which, with the elastic connecting medium, will make an opening of one inch in diameter. Both the rings, however, should be perfectly divided; but a half circle should be excised from one, leaving a portion of cartilage to keep the remainder in its place. This matter, probably, may be made more clear by the engraving on the opposite page.
After the first half circle is made, or when a portion is cut off the first cartilage, that piece should be bent outward. The elastic connecting substance will readily permit this to be done, and the current of fresh air admitted will considerably refresh the animal. The cartilage being bent outward, it should be leisurely transfixed by means of a sharp needle armed with strong twine. The string may be fastened to the button-hole of the operator's waistcoat, and afterward the circle be leisurely completed.
The twine is necessary because the spasmodic breathing has drawn the excised portion of cartilage upon the lungs, and thereby done as much mischief as the operator designed to do good. By bending the half circle outward, some relief is afforded to the breathing, and the character of the respiration partially benefited. The process is, however, rendered more safe by the employment of the loop; but care should be taken, when subsequently using the knife, not to cut the string. Therefore, before the circle is completed, the cartilage should be bent backward, as shown in the previous engraving, then laid hold of, and, when firmly grasped, the excision ought to be perfected.