. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. 100 PHYSIOLOGY AND MORPHOLOGY OF eyeball itself is a much more serious affair. From this arrangement it is evident that motes in the eye can not go beyond easy removal, as it can not go beyond a a', Fig. 70. Muscles.—The nimble movements of the eye are effected by six muscles in each eye. Four of these, the straight muscles (recti), arise near together at the bottom of the conical socket (Fig. 71), come forward diverging, and are attached to the ball a little in front of
. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. 100 PHYSIOLOGY AND MORPHOLOGY OF eyeball itself is a much more serious affair. From this arrangement it is evident that motes in the eye can not go beyond easy removal, as it can not go beyond a a', Fig. 70. Muscles.—The nimble movements of the eye are effected by six muscles in each eye. Four of these, the straight muscles (recti), arise near together at the bottom of the conical socket (Fig. 71), come forward diverging, and are attached to the ball a little in front of the equator, one above (superior rectus), one below (inferior rectus), one on the outside (exterior rectus), and one on the inside (inte- rior rectus). The functions of these are obvious. Each turns the ball in the direction of its pull. When we look upward the two superior recti pull; when we look downward, the two inferior recti. When we look to the right, the external rectus of the right eye and internal rectus of the left eye pull, and vice versa when we look to the left. When we look at a very near object, then the two interior recti pull so as to converge the eyes on the object looked at. But we can not contract the two exterior recti so as to turn both eyes outward, nor can we turn one eye upward and the other downward, because these movements can not serve any useful purpose, and therefore have never been learned. There are two other muscles—the oblique. The supe- rior oblique arises along with the recti at the bottom of the socket, passes forward to the opening of the orbit, Fig. 71.—Muscles of the eyeball: a, optic nerve ; b, superior oblique muscle ; c, pulley; d, in- ferior oblique. The other four are the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original LeConte, Joseph, 1823-1901. N
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