QUESTIONS AND ANSWERS 93 



The clitoris is a small body, two to three inches long, situated 

 in the inferior commissure of the vulva. It is composed of erectile 

 tissue. 



The vulva is the slit-like orifice of the female genitalia and is 

 situated in the perineal region below the anus. 



Organs of Special Sense 

 Describe the eyeball. 



The eyeball, which lies in the fat of the orbit, is a spherical- 

 shaped shell, consisting of three tunics surrounding the humors. 

 It is slightly bulged in front (the cornea), making the antero- 

 posterior, the longest diameter. 



The tunics of the eye are, outer sclerotic and cornea, middle 

 choroid and iris, and inner retina. 



The sclerotic is a white, dense membrane, forming about four- 

 fifths of the external shell, into which the muscles are inserted. It 

 is continued in front as the cornea, a transparent membrane which 

 constitutes the remaining one-fifth of the outer tunic. Posteriorly, 

 the sclera has an opening for the passage of the optic and ciliary 

 nerves and the central artery. 



The choroid, the middle layer, is a thin, brownish, vascular 

 membrane. It is continued anteriorly as the iris, a circular curtain 

 with a central opening, the pupil. This curtain is governed by the 

 ciliary muscle which unites the iris to the sclera. 



The retina, or internal layer, is the thinnest and most delicate. 

 It is the expansion of the optic nerve and adheres closely to the 

 choroid, ending anteriorly in a number of folds, the zone of Zinn. 

 Although very thin, the retina is composed of connective tissue and 

 nerve elements, arranged in nine or ten superposed layers. 



The crystalline lens is a double convex lens of concentric layers, 

 with an external capsule. It is situated in the anterior one-third of 

 the eye, behind the pupil. Back of the lens, filling the space bounded 

 by the retina, is a gelatinous fluid, the vitreous humor, and anterior 

 to the lens is the aqueous humor, which entirely fills the anterior 

 and posterior chamber, the space between the cornea, pupil and iris. 



The eyeball is freely movable in various directions, the move- 

 ments being controlled by seven muscles : five recti and two oblique, 

 all of which attach to the sclera. 



Describe the cornea. 



The cornea is a transparent membrane which constitutes the 

 anterior one-fifth of the outer covering of the eyeball. It is shaped 

 like a watch glass with its convexity forward, and is composed of 



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