78 ANATOMY OF THE HEAD AND NECK. 



which the sclerotic and cornea blend, and it is connectec 

 with the choroid by means of the ciliary muscle. Th< 

 muscular fibres of the iris are unstriated, and are botl 

 circular and radiating. 



The CHAMBERS OF THE AQUEOUS HUMOR are the spac( 

 between the lens behind and the cornea in front, separate 

 by the iris into two compartments, anterior and posterior 

 The anterior chamber is the larger of the two ; their bound: 

 ries will be best seen in an e} 7 e that is bisected longitudi- 

 nally. The aqueous humor is a pure transparent fluid; il 

 disappears by transudation a short time after death. 



The NERVOUS COAT, or the RETINA, requires to be dis- 

 sected in a recent eye; it is the most internal of the three 

 coats of the eyeball and one of the most delicate of its 

 structures ; it lies between the choroid and the vitreous 

 humor, upon which it is moulded. 



The retina may be seen by gently tearing away the choroid in the eye 

 that was used for the examination of that membrane, or by emptying 

 an eye of its vitreous humor after the removal of an anterior segment. 



The retina expands as far forward as the outer edge of 

 the ciliary processes, where it forms a scolloped border, 

 called the ora serrata, and may be traced backward to the 

 lamina cribrosa, the point at which the optic nerve enters 

 the eyeball ; a thin hyaloid membrane, called the zonula 

 ciliaris, or zone of Zinn, is attached to the anterior border 

 of the retina, and continued to the anterior surface of the 

 lens. This membrane, which is composed of folds into 

 which the ciliary processes fit, becomes stained with their 

 pigment, so as to leave a series of radiating lines around 

 the lens. On looking through the vitreous body, the cen- 

 tral artery of the retina wsiy be seen entering b}^ a central 

 foramen in the lamina cribrosa called the porus opticus. 

 A circular spot at the posterior part of the retina is 

 called the foramen of Soemmering; and this is surrounded 

 by a yellow halo called the limbus luteus. 



The CRYSTALLINE LENS lies in a depression in the front of 

 the vitreous humor, and behind the pupil of the iris. It 

 has a proper capsule of transparent membrane, and is held 

 in its place by a suspensory ligament, which is formed 

 by the zonula ciliaris in front and by a similar hyaloid 

 membrane posteriorly, the two uniting behind the ciliary 

 processes; the space between these two layers is called the 

 canal of Petit; this may be demonstrated by the blow-pipe, 



