THE EYE. 7G3 



investigated, although I agree with II. Meyer in the conclusion, that 

 since the tubes, both in the foetus and child, present only a single 

 nucleus, each of them is developed out of a single cell. These nuclei 

 taken as a whole, constitute a thin layer, extending from the borders of 

 the lens, through the middle of its anterior half, and slightly convex in 

 front (" nuclear zone," Meyer) ; the nuclei being smaller in the interior 

 portions, and as it were in progress of solution, whence it may cer- 

 tainly be concluded that the lens increases by the apposition of thin 

 layers from without. The formative cells of the tubes of the lens are 

 those which exist on the anterior half of the capsule and the starting 

 point of the formation of the lenticular elements, according to my 

 observation, is the entire anterior surface and the border of the organ. 

 Nuclei are visible in the tubes even in the lens of the adult, as was 

 known to Harting, though only at its margin. 



With respect to the vessels of the foetal eye, Dr. Thiersch has quite 

 recently communicated to me a mass of interesting details, accompanied 

 by beautiful injections, to which I shall refer in the concluding part of 

 my "Microscopical Anatomy." 



Investigation of the visual organ. The fibrous tunic of the eye 

 should be examined in the recent condition, and in moistened sections 

 of dried preparations, which latter, especially of the cornea and at its 

 point of transition into the sclerotica, afford very useful information. 

 If, after the removal of the vitreous body and lens, the iris and choroid 

 are dried, their connection with each other and with the fibrous tissue may 

 be studied. In order to view the nerves and vessels of the cornea, the 

 latter is removed by a circular section in the recent eye, together with 

 the margin of the sclerotic, the whole is divided into three or four seg- 

 ments, which, in order that they may lie the better, have little incisions 

 made into them around the edge, are moistened with the aqueous 

 humor, and covered with a thin plate. The nervous trunks, which are 

 here usually opaque, are then sought for at the border of the cornea, first 

 with a low power, and afterwards traced under a higher. The nerves 

 are beautifully displayed in the eye of the Rabbit, where I can perceive 

 their trunks with the naked eye, though they may usually be readily 

 found in other eyes also, but are always traced with difficulty towards 

 the centre. If the epithelium is cloudy, it must be removed by caustic 

 soda, which at first does not affect the nerves. The vessels under these 

 circumstances are usually full of blood, and consequently present no 

 difficulties. The corneal epithelium is visible on the surface in sections 

 of dried preparations, and is very well shown when the surface is 

 scraped. The "membrane of Demours" is very distinct in sections, 

 and frequently its epithelium also ; otherwise the latter is well seen on 

 the surface, and in detached shreds of the membrane. The passage of 

 this membrane into the liaamentum pectmatum of the iris, may be seen 



