The lesions of the larynx and trachea are frequently associated with those of the bronchi, more especially the inflammations. Their separation here is consequently somewhat artificial.
Entire Absence of the larynx and trachea occurs only in acephalic monsters which are incapable of living. There are, further, cases of Communication between the trachea and oesophagus. In these cases the pharynx generally ends in a cul-de-sac, and the oesophagus opens into the trachea. Then we meet with cases of imperfect closure of the original branchial clefts leading to the Congenital fistula of the neck, already considered (see p. 53). Again, Individual cartilages, as the epiglottis, or one or more of the rings of the trachea, may be absent, or there may be one or more rings supernumerary. The trachea may divide into three main bronchi instead of two, and in that case two stems pass to the right lung and one to the left. Occasionally the larynx is congenitally narrow, or it may fail to undergo the usual changes at puberty, especially in cases of castration before puberty or of non-descent of the testes. Lastly, the trachea has been observed to the left of the oesophagus or even behind it.