818 PRELIMINARY ANATOMICAL AND HISTOLOGICAL OBSERVATIONS. 



(x). This pigment-layer is lined by the exceedingly delicate limiting membrane 

 of the iris, which is a continuation of the internal limiting membrane of the retina. 

 Within the vascular layer (which contains pigmented connective-tissue cells in 

 bruns) are the two unstriated muscles: the sphincter of the pupil (Fig. 281), 

 which surrounds the pupil, and lies near the posterior surface of the iris (it is 

 innervated by the oculomotor) ; and the dilator of the pupil. The latter consists 



of a thin layer of radially arranged 

 fibers, some of which pass to the 

 pupillary margin, while some bend 

 around into the sphincter. At the 

 outer extremity of the iris the radia- 

 ting fibers are arranged in anastomo- 

 sing arches and form a circular muscle- 

 bundle. The chief nerve of the dilator 

 of the pupil is the sympathetic. 

 Ganglia are found on the ciliary 

 nerves in the choroid. Gerlach has 

 given the appropriate name of avenu- 

 lar ligament of the bulb to the pris- 

 matic bundle of fibrous tissue that 

 bounds the periphery of the iris, and 

 forms the point of union of the ciliary 

 body, the iris, the ciliary muscle, the 

 venous sinus of the iris, and the transi- 

 tion from the cornea to the sclera. 



The course of the choroidal vessels 

 is of great importance for the nutrition 

 of the eye. This is described by 

 Leber as follows : Among the arteries 

 are: (i) The short posterior ciliary 

 (Fig. 267, a, a), about 20 in number, 

 which penetrate the sclera near the 

 optic nerve. They terminate in the 

 vascular network of the chorio-capil- 

 lary layer (w), which reaches as far 

 as the or a serrata. (2) The two long 

 posterior ciliary arteries, one of which 

 lies on the nasal, the other on the tem- 

 poral side. They pass to the ciliary 

 portion of the choroid (6), where they 

 divide dichotomously and enter the 

 iris, to help form the circulus arteriosus 

 iridis major (p). (3) The anterior 

 ciliary arteries (c~), which arise from 

 the muscular branches, perforate the 

 sclera anteriorly, and give off branches 

 to the ciliary portion of the choroid 

 and to the iris. About 12 branches 

 run backward (o) from them to the 

 chorio-capillary layer. The veins 

 carry off the blood as follows: (i) 



FIG. 267. Diagrammatic Representation of the Blood- 

 vessels of the Eye (after Th. Leber). Horizontal 

 section veins dark, arteries light, with a double 

 contour: a, short posterior ciliary, b, long poste- 

 rior ciliary arteries; c c', anterior ciliary artery 

 and vein; d, d', conjunctival artery and vein; 

 e ef, central artery and vein of the retina; /, ves- 

 sels of the inner, g of the outer sheath of the optic 

 nerve; h, vorticose veins; i, short posterior ciliary 

 vein, running only to the sclera; k, branch of the 

 short posterior ciliary artery to the optic nerve; 

 I, anastomosis between the choroidal vessels and 

 those of the nerve; m, chorio-capillary layer; , 

 episcleral branches; o, recurrent rVmrnirlal art*- 



, >, recurrent choroidal artery, 

 p, circulus arteriosus iridis major (cross-section); 

 q, vessels of the iris; r, ciliary process; s, branch 

 of a vorticose vein from the ciliary muscle; /, 

 branch of the anterior ciliary vein from the ciliary 

 muscle; , circulus venosus; v, marginal network 

 ol the corneal limbus; w, anterior conjunctival 

 artery and vein. 



b y ( sthe bi d 



The anterior ciliary veins (c 1 ) receive 

 the blood from the anterior part of 

 the uvea; they pass outward and 

 communicate with Schlemm's canal 

 and Leber's venous plexus. They 

 do not collect any blood from the 

 (2) The venous plexus 



quitearro even SUr / aCe f the lens ' th posterior chamterfs 



b"ue is fnSIed^r, rt t 5 ' an<J I" m ^ ants it; is nearl y obliterated. When Berlin 

 ciUarv veins - P n rS antenor chamber, it almost invariably enters the anterior 

 ary vems, even m living animals; the same is true of carmfne. It is, therefore, 



