Panochthus sp.: Preserved tracheal rings in a Late Pleistocene Glyptodont Mammal from Argentina.
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The trachea of Mammals is a relatively flexible cartilaginous and membranous tube that extends from the cricoid cartilage of the larynx to the middle mediastinum, where it bifurcates into the main bronchi. The framework of the trachea is formed by C-shaped plates of hyaline cartilage ('tracheal rings'. These vary in shape according to the species and in some cases according to the location on the trachea. The number also varies according to the species. The cartilaginous rings provide the tube: some rigidity, otherwise it would collapse as the lungs expand; (ii) some expansion, to be able to accommodate any increase in air volume, by means of the flexibility of the hyaline cartilage, and the dorsal incompleteness of the rings; and (iii) flexibility and extensibility, to be able to follow the movements of the head, neck and larynx. Tracheal cartilages originate from the splanchnic mesoderm and form the true tracheal skeleton.