1060 SPECIAL SENSE ORGANS 



The outer surface of the cornea is covered by an extension of the ocular conjunctiva, in 

 the form of an epithelium several layers deep. The most external part of the true cornea appears 

 homogeneous, even when highly magnified and constitutes the anterior elastic lamina, Bow- 

 man's membrane, though there is reason to believe that its structure only differs from that 

 already described in the closeness of its fibrous texture; the two parts are certainly connected by 

 fine fibres. Posterior^, the cornea is lined by a firm, thin, glass-like layer (posterior elastic 

 lamina, membrane of Descemet), distinct from the corneal tissue both anatomically and chem- 

 ically. At the periphery this membrane breaks up into a number of fibres, which mainly arch 

 over to join the base of the ii-is and form part of the ligamentum pectinatum iridis. The pectin- 

 ate ligament is an open network of interlacing fibres, directly continuous with the circular 

 and longitudinal bundles of sclera smTounding the venous sinus of Schlemm (Henderson). 

 The interstices between these fibres constitute spaces (spaces of Fontana) [spatia anguli iridis 

 (Fontantp)] freely communicating with the aqueous chamber on the one hand, and indirectly 

 with the venous sinus of the sclera on the other. The posterior elastic lamina is in turn lined 

 by a single layer of flat cells, which are continuous peripherally with cells lining the spaces of the 

 angle and the anterior surface of the iris which form the endothelium of the anterior chamber. 

 The cornea is richly supplied with nerves, particularly in its most superficial layers. 



2. The dark, middle, or vascular coat of the eye [tunica vasculosa ocuH] i? 

 formed by the iris, ciliary body, and chorioid. It is closely applied to the sclera, 

 but actually joins it only at the anterior and posterior limits of their course to- 

 gether, viz., at the scleral sulcus, and around the optic nerve entrance. It is 

 separated from the sclera between these two points by a narrow slit-like lymp- 

 space [spatium perichorioideale]. In front of the sulcus, the middle coat is sepa- 

 rated from the outer (i. e., the iris from the cornea) by a considerable space filled 

 with fluid, called the anterior aqueous chamber. The vascular coat has two open- 

 ings in it; a larger one in front, the pupil, and a smaller one behind, for the passage 

 of the optic nerve. Its structure is that of a pigmented connective tissue, support- 

 ing numerous blood-vessels and containing many nerves and three deposits of 

 smooth muscle-fibres. 



The chorioid [chorioidea] forms the posterior part of the vascular coat, and extends, with 

 slowly diminishing thickness, forward as far as the ora serrata. Its outer and inner surfaces 

 are both formed by non-vascular layers; that covering the outer, the lamina suprachorioidea, 

 is pigmented, arranged in several fine loose lamellae; that covering the inner surface is a thin, 

 transparent, homogeneous membrane, called the basal lamina of the chorioid. The inter- 

 vening chorioidal stroma is very rich in blood-vessels, which are of largest size next its outer 

 surface constituting the lamina vasculosa. These become progressively smaller toward the 

 basal lamina, next to which is a layer of closely placed wide capillaries, called the lamina chorio- 

 capillaris. The pigment becomes less in amount as we pass inward, and finally ceases, being 

 absent entirely from the chorio capillary and basal laminae. 



In front of the ora serrata the vascular coat becomes considerably modified' 

 and the part reaching from the ora serrata of the retina to the iris is termed the 

 ciliary region of the tract, or ciliary body [corpus ciliare]. Its superficial aspects 

 have been already briefly described. In front, the ciliary processes, about seventy 

 in number, project toward the interior of the eye, forming the corona ciliaris. Be- 

 hind this part lies the orbiculus ciliaris, whose inner surface is almost smooth, 

 faint radial folds [plicffi ciliarcs] only being present, three or four of which join each 

 ciliary process. 



The more minute structure of this ciliary region resembles closely that of the chorioid, except 

 that the chorio-capillaris is no longer i)resent, that the stroma is thicker and richer in blood- 

 ves.scls, and that a muscular element (ciliary muscle) exists between the vascular layer and th(> 

 lamina siii)rachori<)id('a. On antcro-posterior section the ciliary body is triangular; the shortest 

 side looks forward, and from about its middle the iris arises; the two long sides look respectively 

 inwani and outward, the inner having the ciliary processes upon it, while the outer is formed by 

 the ciliary muscle. This muscle possesses smooth fibres and consists of an outer [fibra> me- 

 ridioiiales (Hruockei)] and an inner division ffibra' circularcs (Mucllcri)]. The meridional fibres 

 take origin from the outer fibrous coat of the eye at the sclero-(^orncal junction in front, and ()ass- 

 ing backward to join the outer layers of the orbiculus ciliaris and chorioid; the circular Al)res 

 are situated next to tlie cihary ))rocesses. The entire muscle is destitute of pigment, and th(>re- 

 fore is rec()gnisal)le in the section by its liglit colour. The whole thick(Miing of the vascular 

 tunic in tliis i-egion, inusck; and folds and processes together, is named the ciliary body. It 

 includes the corona ciharis, formed of the ciliary processes and fohis, and the orl)icularis ciliaris 

 containing the ciliary muscle. 



The iris projects into the interior of the front half of the eye in the form of a 

 circular disc perforated in the middle. The ajijx^arance of its anterior surface has 

 already Ix'cn described. The anterior surface is cover(Ml with a layi^r of endothe- 

 lium excei)t at the cryi)ts near the ciliary l)ord{>r. 'I'lius the lym])h spaces between 

 the stroma cells communicate (lircclly with the anterior chamber. Its posterior 



