SECT. 230.] TISSUES OF THE EYE. 58 I 



child, each presents only a single nucleus; and, from this fact, 

 I concur with 77. Meyer in drawing the conclusion, that each of 

 the fibres is developed from a single cell. These nuclei, considered 

 in their totality, form a thin layer, proceeding from the margin of 

 the lens through its anterior half, and having a slight convexity 

 forwards (nuclear zone of Meyer) ; while in the inner parts, the 

 nuclei are smaller, as if in the act of dissolution, whence it may 

 be concluded that the lens grows from without by the apposition 

 of thin laminae. The cells which go to form the tubules of the 

 leus are those which are situated at the anterior half of the cap- 

 side; and, from what I have seen, the starting-point in the 

 formation of the elements of the lens is at the border of the organ. 

 Even in the lens of the adult, as I have shown (Micr. Anat., ii., 2, 

 p. 730, et seq.), all stages of development in the fibres of the lens 

 (fig. 238) may be seen at the border of the organ, and we can at 

 the same time convince ourselves that the fibres really arise from 

 the cells of the epithelium. 



Investigation of the Organ of Vision. — The fibrous coat of the eye is to be 

 examined in its fresh state, and in softened sections of dried preparations ; 

 the latter especially give good views of the cornea, and of its transition into 

 the sclerotic. If, after the removal of the vitreous body and lens, the iris and 

 chorioidea be dried together, their connection with each other and with the 

 fibrous tunic, may also be studied. In order to see the nerves and vessels of 

 the cornea, the cornea of a fresh eye is to be cut off, along with the border 

 of the sclerotic, by means of a circular section, and the whole is then to be 

 divided into three or four segments ; they should then be notched at the cut 

 edges, in order to lay them flat, moistened with the aqueous humour, and 

 covered with a glass plate. The nervous trunks, which are mostly dark in this 

 situation, are first to be sought with low magnifying powers at the border of 

 the cornea, and then traced onwards with stronger lenses. The nerves are 

 most beautiful in the eye of the rabbit, where I can recognise their trunks 

 with the naked eye; but they can also, as a rule, be readily found in other 

 eyes, though they are always difficult to trace towards the middle. If the 

 epithelium is turbid, it must be removed by caustic soda, which does not at 

 first alter the nerves. The vessels are mostly found filled with blood, and 

 present no difficulties. The epithelium of the cornea is seen very well from 

 the surface on sections of dried preparations, and also by scraping it off. 

 The membrane of Demours is very distinct in sections, and sometimes its 

 epithelium, too ; or the latter may be very well seen from the surface, or on 

 detached shreds of the membrane. The transition of this membrane into 

 the ligamentum iridis pectinatum, is recognised upon sections and by careful 

 dissection. In the latter case, the iris and the choroid must be detached, 

 and the inner wall of the canal of Sehlemm is to be carefully removed along 

 with them; portions of the membrane of Demours may then often be 

 separated without difficulty. The uvea presents but little difficulty. The 

 pigment-cells of the struma, with their processes and the internal pigment, 



