THE EYE. 725 



AYharton Jones, " The blood-corpuscle considered in its diff. phases of 

 development," in the " Phil. Trans.," 184G, IL, p. 82. Besides which 

 should be consulted the hand-books of E. 11. Weber and Henle, and 

 the recent embryological works of Vogt, Remak, Provost, Lebert, and 

 Courty. [The more recent publications on the vascular system are : 

 Von Ilessling " Ilistologische Mittheilungen," in Siebold and Kolli- 

 ker's Zeitschrift, v., p. 189 ; A. Kollikcr, " Ueber den feinern Bau 

 11. die Functionen der Lymphdrlisen," in " Verb d. pbys. med. Ges. in 

 Wurzb.," iv. 2, 1854; Rokitansky, "Ueber einige der wichtigsten 

 Krankhciten der Arterien," Wien, 1852; C. Wedl, "Ueber Blut. u. 

 Blutgefiiss Neubildung," in "Schmidt's JahrbUcher," No. 12, 1853; J. 

 Moleschott, " Ueber das Verhiiltniss der farblosen Blutzellen zu den 

 farbigen in verschiedenen Zustiindon des Menschen," in " Wiener 

 Mediz. Wochenbl." No. 8, 1854 ; T. Williams, " On the Blood proper 

 and the Chylaqueous Fluid of Invertebrate Animals," in "Phil. 

 Trans.," part ii., 1853, and " The Blood, its Chemistry, Physiology, 

 and Pathology," in British and Foreign Med. Chirurg. Review, Oct. 

 1853, and Jan. 1854.— DaC] 



OF THE HIGHER ORGANS OF SENSE. 



I. OF THE OPtGAN OF VISION. 



§ 224. The visual organ consists of the eT/eball, or the proper sensi- 

 tive apparatus, and the accessor?/ parts, some for its protection, some for 

 its movement: viz. the eyelids, the ocular muscles, and the lachrymal 

 organs. The eyehall itself is a very complex organ, into the constitu- 

 tion of which nearly all the tissues of the body enter. It is composed 

 essentially of three tunics : ti fibrous — the sclerotica and cornea, a vas- 

 cular — the chorioidea and iris, and a 7iervous ; and of two internal 

 refractive media — the vitreous humor and the crystalline lens. . 



A. OF THE EYEBALL. 



§ 225. Fibrosis tunic of the Eye. — The external envelop of the eye- 

 ball is formed by a tough, fibrous membrane, composed chiefly of 

 connective tissue, which, to outward appearance, is divisible into a 

 smaller, anterior, transparent portion — the cornea; and a larger, 

 opaque, posterior part — the sclerotic ; but, as shown by its development 

 and more intimate structure, is to be regarded as a membrane continu- 

 ous throughout. 



The sclerotica, also termed the tunica albuginca, is a white, very 

 tough and strong, fibrous membrane, which gradually diminishes in 

 thickness as it advances forwards from the posterior part of the eye, 



