Henry Gray (18251861). Anatomy of the Human Body. 1918.
Posteriorly it is limited by the mucous membrane passing between the arytenoid cartilages. The rima glottidis is the narrowest part of the cavity of the larynx, and its level corresponds with the bases of the arytenoid cartilages. Its length, in the male, is about 23 mm.; in the female from 17 to 18 mm. The width and shape of the rima glottidis vary with the movements of the vocal folds and arytenoid cartilages during respiration and phonation. In the condition of rest, i. e., when these structures are uninfluenced by muscular action, as in quiet respiration, the intramembranous part is triangular, with its apex in front and its base behindthe latter being represented by a line, about 8 mm. long, connecting the anterior ends of the vocal processes, while the medial surfaces of the arytenoids are parallel to each other, and hence the intercartilaginous part is rectangular. During extreme adduction of the vocal folds, as in the emission of a high note, the intramembranous part is reduced to a linear slit by the apposition of the vocal folds, while the intercartilaginous part is triangular, its apex corresponding to the anterior ends of the vocal processes of the arytenoids, which are approximated by the medial rotation of the cartilages. Conversely in extreme abduction of the vocal folds, as in forced inspiration, the arytenoids and their vocal processes are rotated lateralward, and the intercartilaginous part is triangular in shape but with its apex directed backward. In this condition the entire glottis is somewhat lozenge-shaped, the sides of the intramembranous part diverging from before backward, those of the intercartilaginous part diverging from behind forwardthe widest part of the aperture corresponding with the attachments of the vocal folds to the vocal processes.
Muscles.The muscles of the larynx are extrinsic, passing between the larynx and parts aroundthese have been described in the section on Myology; and intrinsic, confined entirely to the larynx.
The intrinsic muscles are:
The Cricothyreoideus (Cricothyroid) (Fig. 957), triangular in form, arises from the front and lateral part of the cricoid cartilage; its fibers diverge, and are arranged in two groups. The lower fibers constitute a pars obliqua and slant backward and lateralward to the anterior border of the inferior cornu; the anterior fibers, forming a pars recta, run upward, backward, and lateralward to the posterior part of the lower border of the lamina of the thyroid cartilage.