Functional anatomy of the musculature of the trachea

The smooth musculature of the human trachea was studied and compared with earlier observations in the rabbit. The results may be summarized as follows: 1. The annular m. constrictor tracheae, previously observed in the rabbit, has also been identified in the human trachea. 2. Longitudinal muscle fibers outside the constrictor musculature were observed in man. These fibers are rudimentary and appear to be of no functional importance. 3. From a functional point of view, it appears justified to regard the outer tracheal musculature largely as a constrictor musculature. 4. The main function of the outer musculature of the trachea and the elastic cartilaginous arches is to maintain the stability of the tracheal wall. 5. The variation of the lumen of the trachea is mainly controlled by the m. trachealis in the pars membranacea.