CAVITY OF THE ORBIT in:;.; 



posterior <>f these chambers liy tnmsudat ion from the vessels of the ciliary bod v and 

 posterior surf ace of the iris (eee ako page loiioi. '1 lie M ream \ nl\ foruards 



through the pupil into the anterior aqucou.-. chainher, whence it escapes slowly liv 

 passing through the spaces 01 FontMia into Schlemm's canal, and I hence im,', df,. 

 anterior ciliary veins. 1'art of the lympli-st n am pas>es from the posterior aqueous 

 chamber backuards into the xonular space (canal of Petit), out of which fluid can 

 pass into the lens substance, or diffuse itself into (he front of the vitreous. 



In the cornea the lymph travels in ti. already mentioned as existing 



the fibre-bundles, and in the nerve-channels and at the periphery of the 

 cornea it Hows off into the lymphatic \essels of the conjunctiva. 



In the iris there is a system of lymphatic spaces opening anteriorly on its free 

 surface by the crypts previously described, and communicating peripherally with 

 - of Font ana. 



2. Posteriorly, we have (a) the central or hyaloid canal, between the | 

 rior pole of the lens and the optic nerve entrance, and (6) the [>erivascular canals 

 of the retina; the lymph from both of these situations flows into the span s of the 

 optic nerve, which communicate with the intervagimil space of the nerve, and thus 

 with the great intracranial spaces. Further, between chorioid and sclerotic we 

 have (e) the perichorioidal space, which gets the lymph from the chorioid. and com- 

 municates with Tenon's space outside the sclerotic by the perforations corresponding 

 to the vasa vorticosa and posterior ciliary arteries, and with the intervaginal 8] 

 around the optic nerve entrance. Tenon's space, attain, is continuous with the 

 supnivaginal space around the optic nerve, which communicates both with the 

 intervaginal spaces, with the lymph-spaces of the orbit, and directly with the intra- 

 eranial spaces at the apex of the orbit. 



The development of the eye. Three different embryonic tissues take part in the for- 

 mation of the eye, namely, an outgrowth from the contra! nervous system, an invagination of 



the surface ectoderm, .-MM! the incsnilcnii tissue in tljc vicinity of these t\\o si ructures. From 

 the outgrowth from the l>rain the retina in all its parts and the optic nerve develope, from (lie 

 surface invagination the lens, and the remaining .structures an- formed from the nic.-oderm. 

 The vitreous may also possibly have a partial origin from the primitive retinal tissue.-. 



The central outgrowth takes the form of a hollow bulb attached to the brain by a long slen- 

 der stalk. When by its growth it comes into contact with the lens invagination. the outer half 

 of the bulb sinks back into its cavity until it conies into contact with the wall of the posterior 

 half, and the bulb is thus converted into a cup. But the cup i* an incomplete one, for its entire 

 ventral wall and a portion also .if that of the stalk become pushed up into the cavities of : 

 structures, so that along their ventral surfaces there is a deep fissure known as the chorioidai fix- 

 sure. In normal development the fissure is eventually obliterated by the union of its lips, but 

 occasionally it persists more or less completely, producing the condition known as coloboma. 



In the fissure an artery and vein develope and so reach the cavity of the optic cup. AVhen 

 the fissure closes they become enclosed and form the arteria and vena contrails retina'. In 

 the embryonic condition branches from these vessels extend through the vitreous and form a 

 vascular tissue almost completely investing the lens, which occupies the mouth of the cup. 

 These hyaloid vessels normally disappear later, leaving only the hyaloid canal as a reminder 

 of their existence, but occasionally traces of them may persist over the anterior surface of the 

 lens, forming what is termed a persistent pupillary membrane, or in the vitreous as a persistent 

 hyaloid artery. 



CAVITY OF THE ORBIT 



GENERAL ARRANGEMENT OF ITS CONTENTS 



The anterior wider half of the cavity is mainly occupied by the eyeball, which 

 lies almost axially, but is rather nearer to the upper and outer than it is to the 

 other walls. The posterior two-thirds of the globe are in relation with soft parts, 

 chiefly muscles and fat, and its posterior pole is situated midway between the base 

 for opening) and the apex of the orbital cavity. The anterior third of the eye- 

 ball is naturally free, except for a thin covering of the conjunctiva, and proi. 

 slightly beyond the owning of the orbit, the degree of prominence varying with 

 the amount of orbital fat. and a No to some extent with the length of the globe. A 

 straight line joining the inner and outer orbital margins usually cuts the eye behind 

 the cornea externally behind the ora serrata. nasally further forwards, at the 

 junction of the ciliary body and iris. The globe is held in position by numerous 

 bands of connective tissue. The lachrymal gland lies under the outer part of the 

 roof of the orbit, anteriorly. The orbital fat occupies the spaces between the orbital 



