196 



nerve, which, without communicating with the other two, 

 opens directly into the arachnoidal sac of the brain. 



Between the inner surface of the sclerotica and the outer 

 layer of the choroid is a space, which was recognised by 

 Arnold as a serous cavity, and to which the name arachnoidea 

 oculi might be given. It is, however, occupied in part by some 

 loose connective tissue with elastic fibres and stellate pig- 

 ment-cells, which constitute the membrana supra-choroidea 

 of Henle, and the lamina fusca of most anatomists. This is 

 quite a distinct structure from the space or sac itself, and 

 need not now be considered. The cavity itself, called by 

 Schwalbe the perichoroid space, has the closest resemblance 

 to the lymphatic sac of the frog, having inner surfaces, which 

 even to tlie naked eye are sometimes smooth and shining, and 

 are found, on careful examination, to show on both surfaces 

 the epithelial markings characteristic of lymphatic spaces. 

 The principal method made use of to demonstrate this struc- 

 ture Avas tlie silver method of Recklinghausen, which had the 

 effect of bringing into view a complete epithelial network, in 

 the meshes of which wei'e contained oval nuclei. No means 

 was found of isolating the epithelial forms, but even without 

 the silver treatment little shreds of membrane containing nuclei 

 could be torn off. These appearances were best seen in the 

 eyes of white rabbits, Avith more difficulty in pigmented eyes, 

 and not at all in the human eye, since a specimen of this 

 could never be obtained in a sufficiently fresh state. The 

 perichoroid space being thus defined, injections were made 

 into it with the view of determining its extent and connec- 

 tions. When completely filled with a coloured liquid the 

 space was found to reach backward into the neighbourhood 

 of the entrance of the optic nerve, and forward as far as just 

 under the ciliary processes. The space thus forms a complete 

 double envelope, surrounding nearly the whole of the eyeball. 

 The injection never penetrated into the proper vascular tissue 

 of the choroid, or into any of the chambers of the eye ; it did, 

 however, leave the space at four points, and these are points 

 corresponding to the entrance of the venae vorticosoe. It has 

 been clearly made out that the injection passed through 

 spaces encircling the veins, which, on a cross-section, were 

 found completely surrounded by it. Through these perivas- 

 cular canals the perichoroid space communicates with the 

 space between the eyeball and the capsule or fascia of Tenon, 

 which may be called the space of Tenon ; and this was filled 

 with injection from the perichoroid space. The space of 

 Tenon further comnuniicatcs backwards by a cylindrical 

 channel surrounding the outer fascia of the optic nerve with 



