A manual of anatomy . ant behind that organ. THE EYEBALL The eyeball {bulbus oculi) occupies the anterior portion of the orbitbeing protected by the orbital margins and the eyelids. The antero-posterior and the transverse diameters are 24 mm. while the verticaldiameter is mm. so that the eyeball is not quite a sphere at theequator. At birth the eyeball is about mm. in diameter and is THE CORNEA 343 nearly spherical in shape. It increases about 3 mm. between birthand puberty and soon thereafter attains its adult size and shape. The apparent difference in the size of the eyeballs of di
A manual of anatomy . ant behind that organ. THE EYEBALL The eyeball {bulbus oculi) occupies the anterior portion of the orbitbeing protected by the orbital margins and the eyelids. The antero-posterior and the transverse diameters are 24 mm. while the verticaldiameter is mm. so that the eyeball is not quite a sphere at theequator. At birth the eyeball is about mm. in diameter and is THE CORNEA 343 nearly spherical in shape. It increases about 3 mm. between birthand puberty and soon thereafter attains its adult size and shape. The apparent difference in the size of the eyeballs of difierentindividuals is not due to a real difference in size but to a differencein the prominence of the eyeball and width of the palpebral viewed from the side the eyeball is seen to consist of parts oftwo spheres. The smaller, anterior, corneal portion (about one-sixth) represents part of a sphere of 14 mm. diameter, while thelarger, posterior portion (five-sixths), represents the greater part of ,P«« axis Fig. 253.—Horizontal section of the right eyeball. a sphere of 24 mm. diameter. The optic axis is represented by aline connecting the anterior and posterior poles, that is the centralpoints of anterior and posterior curvatures, respectively. Theequator is the line around the eyeball midway between the visual axis is a line that passes from the first nodal point of thecornea to the fovea centralis of the retina. The eyeball is called the organ of vision {organon visus). Inreality it makes an image like a camera, while nerve impulses thatare generated by the cells of the retina travel to the brain and theseimpulses are then translated into photic impressions. The eyeball consists of three coats, or tunics: (i) the corneoscleral[tunica fibrosa oculi); (2) the choroid, ciliary body and iris, or theuveal tract; (3) the retina. I. The cornea constitutes about one-sLxth of the circumference ofthe eyeball and is transparent. It represents one of the impo
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecthumananatomy, bookyea
