In the course of the preceding observations we have already noticed some of these processes; others still require to be described. Their position is, with very few exceptions, in the larynx and trachea, and as they are generally the result of a process originally proceeding from the mucous membrane, the direction of their destroying course is inwards into the tissues, and, as a rule, they make their way from within outwards.

Those we have already described are catarrhal suppuration, the sloughing ulcer, which, with the aphthous ulcer, must be regarded as degenerate exudative processes, the variolous ulcer, and the typhous ulcer; also the suppuration and necrosis of the mucous membrane, proceeding from the submucous areolar tissue. We have yet to consider suppuration of the perichondrium with necrosis of the laryngeal cartilages, and tuberculous and cancerous ulceration.

We must here notice syphilitic ulceration of the air-passages. Ulcers of this nature are, for the most part, situated on the epiglottis, having extended there from the soft palate and the root of the tongue. They usually present the characters of secondary chancres, and not unfre-quently give rise to entire destruction of the epiglottis and of the mucous membrane around the glottis. The syphilitic destruction usually confines itself to these parts, leaving, after cure, a loss of part of the epiglottis, and thick, hard, white, tendinous, and cord-like cicatrices, crossing one another and giving rise to contraction. In rare cases, however, they extend to the larynx and trachea, and destroy the mucous membrane by causing sloughing and aphthae, giving rise to contraction of the submucous tissue, and to friability and brittleness of the cartilages.

The walls of the air-passages are also liable to ulceration from without inwards. This occurs by far the most frequently in the bronchi, in consequence of their frequent proximity to softened tubercle and to tuberculous abscesses.