SECTS. 223, 224.] ORGAN OF VISION. 537 



( I tabular. Sanguinis Origine, Turioi, 1845. A. Kolliker, in Zeitschr.f. rat. 

 Med., bd. iv., 1846, p. 4.2. C. Donders and J. Moleschott, in d, Holldndischen 

 Beitr'dgcn,m. p. 360. Donders, in Ned, Lancet, 1846. W.Jones, in Phil. 

 Trans., 1846, ii. p. 82. Moleschott, in Mull. Arch., 1853 ; then in Wien. Med. 

 Wochenschr., 1853, April, and 1854, Feb. Vierordt, in Arch.f. Phys. Eeilk, 

 xi. Kolliker, in Zeitschr.f. w. Zool., vii. pp. 182, 183 ; also in Wiirzb. Verh., 

 vii. E. A. Hirt, De Copia rel. Corp. Sanguinis Alborum, Diss., 1855, Lips. ; 

 and in Mull. Arch., 1856, p. 174. Aubert, in Zeitschr.f. w. Zool., vii. p. 357. 

 Stoltzing, Uebcr Zahl d. Blutltorp. Marb., 1856, Diss. Lorange, Quoin, rat. 

 cell. sang. alb. et mbr. matet. oibor. advect., Diss. Regiom., 1856. Berlin, in 

 Ned. Lane, 3 ser., v. jaarg., p. 734 5 and Arch.f. Holl. Beitr., i. p. 75. Marfels 

 and Moleschott, in Untersuch, z. Naturl., i. p. 52. Teichmann, in Zeitschr. 

 f. rat. Med., viii. p. 141. — Reference should also be made to the Manuals of 

 E. H. Weber and Henle, and to the recent works on Embryology of Vogt, 

 Remak, Prevost, Lebert, and Courty. 



OF THE HIGHER ORGANS OF SENSE. 



I. Of the Organ of Vision. 



§ 223. The organ of vision consists of the eye-hall, or the proper 

 sensory apparatus, together with certain accessory parts, which are 

 present partly for its protection, partly for its movement ; these 

 are, the eye-lids, the muscles of the eye, and the lachrymal organs. 

 The eye-ball itself is a very complex organ, in which almost all the 

 tissues of the body are represented ; and it is essentially composed 

 of two internal refracting media, the vitreous body and the lens, 

 together with three coats or tunics : the outermost fibrous, com- 

 prising the sclerotica and cornea; the next vascular, the choroid 

 with the iris ; and the third is the nervous coat. 



A. OF THE EYE-BALL. 



§ 224. Fibrous Tunic of the Eye. — The external envelope of the 

 eve-ball is formed by a dense fibrous tunic, which, to outward 

 appearance, is subdivided into a smaller, anterior section, the cor- 

 nea, which is transparent; and into a larger, posterior, opaque part, 

 the sclerotic, although the whole is to be regarded as a single 

 connected tunic, as is proved by its development as well as by its 

 intimate structure. 



The sclerotic coat, also called the tunica albucjinea, is a white, 

 fibrous membrane, very dense and firm, which is thickest at the 



