2 
Henry L. Bruner 6 
As observed by Leydig, 72, p. 81, the smooth muscle of the orbit has 
nothing to do with the ordinary winking movements, which are confined 
to the lower eyelid. Leydig assigns to the muscle the function of expel- 
ling the glandular secretions of the eye. Weber, 77, concludes, from the 
distribution of the muscle fibers in the eyelids, that the muscle is used 
to drive out the lymph from the sinuses of the lids. The latter view is 
undoubtedly correct, in so far as it concerns the palpebral portions of the 
muscle. This function, however, does not explain the existence of the 
deeper part of the muscle, to which another office must be assigned, 
namely, the compression and reduction of the flooded sinus orbitalis. 
Such a function is clearly indicated by the direction of the fibers and by 
their relation to the sinus orbitalis. 
It is not improbable, especially in view of the character of the muscle, 
that it maintains, under ordinary circumstances, a certain tonus and 
thus assists in preserving normal conditions in the sinus orbitalis. The 
relaxation of the muscle would, therefore, facilitate the flooding of the 
sinus orbitalis, after the contraction of the m. constrictor venze jugu- 
laris interne. 
In addition to the functions just described the m. compressor sinus 
orbitalis produces certain peculiar movements of the eyelids. In a 
specimen of Sceloporus undulatus, for example, a peculiar contortion of 
the upper lid was noted, the movement beginning at the anterior canthus 
and advancing wave-like toward the posterior canthus. The progress of 
the movement was slow and resembled the movements which occur at 
the external nares. Since the upper eyelid is provided only with smooth 
muscle fibers from the m. compressor sinus orbitalis, that muscle must 
be the cause of the movement. Similar movements which were observed 
in the lower eyelid are undoubtedly to be attributed to the same muscle. 
b. REDUCTION OF THE SINUS ORBITALIS. 
If the relaxation of the orbital muscles facilitates the flooding of the 
sinus orbitalis, the contraction of these muscles, after the sinus has been 
flooded, must accelerate the escape of blood and assist in reducing the 
sinus to its ordinary condition. The contraction of the bulbus muscles 
forces the blood especially from the deeper parts of the orbit, while the 
smooth orbital muscle, m. compressor sinus orbitalis, exerts a pressure 
throughout the entire orbit, expelling the blood both from the sinus 
orbitalis and from the sinus membrane nictitantis, and reducing the 
swollen eyelids by compression of the great lymph-sinuses. 
In these changes the m. depressor palpebre inferioris also plays a part 
