An anatomic study of the check mechanism of the vertical muscles of the eye.

Although our knowledge of the check mechanism of the horizontal muscles is fairly well established, very little positive evidence is available as to the check mech­ anism associated with the vertical muscles. This is understandable when one considers the greater complexity in the anatomic ar­ rangement of the vertical muscles as com­ pared with the horizontal muscles. With the hope of obtaining a clearer con­ cept of the check mechanism of the vertical muscles, I have assembled some anatomic data pertaining to this subject. It is obvi­ ously not feasible to present a complete de­ scription of the check mechanism based on an anatomic study only. However, such a study may serve as a basis for further work, which will lead to a better understanding of this complex problem. The investigation is based on the study of a series of chemically prepared anatomic specimens, and supplemented by the exam­ ination of living tissues of patients requir­ ing an enucleation or muscle surgery. The living tissue presents a more accurate pic­ ture of the anatomy than can be found in the laboratory specimens. For the purpose of presentation, the sub­ ject will be divided into two parts: first, the anatomic structures involved, and sec­ ond, the role of these structures in the check action of the vertical muscles. The understanding of the check action of a vertical muscle necessitates a clear concept of the anatomy of the area. The following is a review of the anatomy of the fascial membranes associated with the various vertical muscles. A familiarity with the anatomy of the vertical muscles is assumed. Although the levator muscle, strictly speaking, is outside the scope of this paper, its close association in the check action of the vertical extrinsic muscles necessitates its inclusion in an anatomic description of the area. The posterior half of the levator muscle, for the most part, is devoid of a condensed membrane, being covered by only a thin mesh of fibro-elastic tissue which binds the muscle fibers to the surrounding reticulum of fatty tissue. In fact, this membrane over the posterior half of the muscle is so thin that the muscle fibers appear practically devoid of covering. Anteriorly, however, the fascial .sheath becomes gradually thicker and more evident until, just posterior to the aponeurosis, the whole muscle is enveloped in a thick, opaque sheath (fig. 1). This sheath on the upper aspect of the …