Here we must mention the acquired malformation to which the larynx, trachea, and bronchi are subject, occurring in the form of flattening, indenting, or curving from a morbid and enlarged thyroid gland, an encysted tumor, or an aneurism, or in consequence of cicatrization after destructive ulceration.

The epiglottis is especially liable to present remarkable anomalies, being found irregularly flattened, and with its edges immoderately sloped or bent backwards, turned down, or rolled together like a horn. These malformations are either the consequence of the contraction of cicatrices in the mucous membrane, submucous areolar tissue, or its actual substance, or of inflammation of its cartilage, with consecutive softening or induration and atrophy of its substance, converting it into a rigid fibrous tissue.

4. Deviations Of Position

These principally occur in the larynx and trachea, which may be forced from their perpendicular direction in the neck to either side of the vertical line by partial enlargement of the thyroid gland, by encysted tumors on the side of the neck, by aneurisms, abscesses, cancerous deposits, or wry neck; they may be displaced forwards by swollen and inflamed cervical vertebrae, and by abscesses seated in them; whilst they may be thrust backwards into the dorsal curvature of the vertebral column by aneurisms of the arch of the aorta, cancerous deposits in the anterior mediastinum, etc.

The occasional but rare dislocations of the laryngeal articulations, must also be mentioned as a cause of deviation of position.

5. Interruptions Of Continuity

We must here take into consideration: a. The various injuries of the air-passages from cutting or stabbing instruments, gun-shot wounds, fractures and minor injuries of the hyoid bone and laryngeal and tracheal cartilages; also lacerations in consequence of forcible concussions or contusions; and, finally, injuries, arising from the entrance from without of angular and pointed foreign bodies into the aforesaid air-passages.

b. The gradual solutions of continuity in consequence of atrophy, especially induced by the continuous pressure of aneurisms; and c. The numerous separations of continuity dependent on various ulcerous processes acting either from within outwards, or in the opposite direction.

All of these, more or less rapidly, give rise to abnormal communications between the air-passages and the surrounding areolar tissue, and (continuing their progress externally) connect the former with the adjacent cavities and canals, as with the pleural sacs, bloodvessels, or oesophagus, or with abscesses in the lungs, bronchial glands, vertebrae, or lateral and anterior walls of the thorax, allowing not only the passage of air in various directions from the respiratory organs, but also the far more perilous entrance of blood, purulent and ichorous fluids, food and drink into them.

(We might here consider the congenital cervical fistulae described by Dzondi, Ascherson, Serres, and others. They are certain anomalies of original formation; but we still require more precise information regarding their mode of development and their signification).